Chemistry

Chemical Equilibrium

⚖️ Chapter · MDCAT Chemistry
📅 Updated Jan 2026 ⏱️ 30 min read 🎯 High-yield

Chemical Equilibrium — Complete MDCAT Notes & MCQs

Full MDCAT Chemistry notes on chemical equilibrium: reversible reactions, dynamic equilibrium, Kc and Kp, Le Chatelier's principle (concentration, pressure, temperature, catalyst), solubility product (Ksp), common ion effect, buffer solutions (Henderson-Hasselbalch), and the Haber process for ammonia synthesis. Includes 200 solved MCQs with explanations and year-wise past papers.

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⚡Quick Answers to Common Searches

Direct, snippet-optimized answers to the top questions students search about Chemical Equilibrium.

What is chemical equilibrium?

Chemical equilibrium is the state in a reversible reaction when the rate of forward reaction equals the rate of reverse reaction. Concentrations remain constant (dynamic equilibrium).

Macroscopic characteristics?

Closed system, concentrations constant over time, and measurable properties like colour, density, and pressure unchanged — though molecular processes continue.

What is Le Chatelier's principle?

If a system at equilibrium is stressed, it shifts in a direction that counteracts the imposed change (concentration, pressure, temperature).

What is Kc?

Kc is the ratio of product concentrations to reactant concentrations, each raised to their stoichiometric coefficients. Depends only on temperature.

Kc vs Kp relationship?

Kp = Kc(RT)^Δn, where Δn = (moles of gaseous products) − (moles of gaseous reactants).

Large vs small Kc?

Large Kc (>1): products favoured (reaction nearly complete). Small Kc (<1): reactants favoured.

What is Ksp?

Ksp is the solubility product constant for a sparingly soluble salt. Depends only on temperature.

Common ion effect?

Decrease in solubility of a salt when a second compound containing one of the same ions is present. Explained by Le Chatelier's principle.

What is a buffer?

A solution that resists pH change when small amounts of acid or base are added. Acidic buffer: pH <7. Basic buffer: pH >7.

Henderson-Hasselbalch equation?

Acidic buffer: pH = pKa + log([A⁻]/[HA]). Basic buffer: pOH = pKb + log([salt]/[base]).

Maximum buffer capacity?

At [Salt] = [Acid] (or [Base]), i.e., when pH = pKa (or pOH = pKb).

What is Haber process?

Industrial synthesis of ammonia: N₂ + 3H₂ ⇌ 2NH₃ (ΔH = −92 kJ). High P (200-300 atm), moderate T (450°C), Fe catalyst.

Effect of catalyst on equilibrium?

No effect on equilibrium position or K. Only speeds up reaching equilibrium.

Effect of inert gas?

Constant volume: no shift. Constant pressure: shifts toward more moles of gas (volume increases).

How many MCQs from Equilibrium?

Chemical Equilibrium typically contributes 3–5 MCQs out of 81 Chemistry MCQs in MDCAT.

❓People Also Ask — Chemical Equilibrium

Questions students most frequently search about this chapter. Answers are direct and exam-focused.

QWhy is equilibrium called dynamic?
Equilibrium is called dynamic because both forward and reverse reactions continue occurring at the same rate — nothing appears to change at the macroscopic level, but reactions are happening at the molecular level.
QHow does temperature affect Kc?
For exothermic reactions: increasing T decreases Kc. For endothermic reactions: increasing T increases Kc. Kc changes only with temperature — not with concentration, pressure, or catalyst.
QWhat is the difference between Q and K?
Q (reaction quotient) uses current concentrations at any time. Kc is measured at equilibrium. If Q < Kc → reaction proceeds forward; if Q > Kc → reverse; if Q = Kc → system at equilibrium.
QDoes pressure affect all equilibria?
Only gaseous equilibria where Δn ≠ 0 are affected by pressure. If moles of gas are equal on both sides (e.g., H₂ + I₂ ⇌ 2HI, Δn = 0), pressure has no effect on equilibrium position.
QHow is Ksp calculated from solubility?
For salt A_mB_n with solubility 's': Ksp = (ms)^m × (ns)^n. For example, AgCl: Ksp = s². CaF₂: Ksp = 4s³. Ca₃(PO₄)₂: Ksp = 108s⁵.
QWhen does precipitation occur?
Precipitation occurs when the ionic product (Qsp) exceeds Ksp (Qsp > Ksp). If Qsp < Ksp, solution is unsaturated. If Qsp = Ksp, saturated (no precipitation).
QWhat is the common ion effect?
The common ion effect is the decrease in solubility of a salt when another compound containing one of the same ions is added. E.g., adding NaCl to saturated PbCl₂ reduces PbCl₂ solubility. Used in qualitative salt analysis (Group II precipitation).
QWhat is a buffer solution?
A buffer is a solution that resists change in pH when small amounts of strong acid or base are added. Made from a weak acid and its salt with strong base (acidic buffer), or weak base and its salt with strong acid (basic buffer).
QWhat is the pH of blood?
Blood pH is maintained at ~7.4 by the H₂CO₃/HCO₃⁻ buffer system. Deviations cause acidosis (pH <7.35) or alkalosis (pH >7.45), both life-threatening.
QWhy is buffer capacity maximum at pH = pKa?
At [HA] = [A⁻], the buffer can neutralize added acid or base equally well from both directions. This gives maximum resistance to pH change (buffer capacity β is maximum).
QWhat happens when buffer is diluted?
When a buffer is diluted, the pH remains nearly unchanged (ratio [A⁻]/[HA] stays same), but the buffer capacity decreases because total concentration is lower.
QWhy is Haber process temperature compromise at 450°C?
The reaction is exothermic, so low T favours NH₃ yield (Le Chatelier). But low T is too slow kinetically. 450°C balances high yield at an acceptable rate — a compromise temperature.
QWhy high pressure in Haber process?
N₂ + 3H₂ ⇌ 2NH₃ has 4 moles of gas → 2 moles. Increasing pressure shifts equilibrium toward the side with fewer moles (products). 200-300 atm favours NH₃.
QWhat is the role of promoters in Haber process?
Promoters like K₂O and Al₂O₃ enhance iron catalyst activity: K₂O increases electron transfer to N₂; Al₂O₃ prevents iron sintering (clumping) at high temperature.
QWhy is NH₃ removed from Haber reactor?
Removing NH₃ (by liquefaction) shifts equilibrium forward (Le Chatelier) — product removal favours the forward reaction. Unreacted N₂ and H₂ are recycled.
QDoes adding a solid shift equilibrium?
No. Pure solids and pure liquids have constant activity (defined as 1) and don't affect equilibrium position. E.g., adding CaCO₃(s) to CaCO₃ ⇌ CaO + CO₂ does nothing.
QWhat is ΔG° at equilibrium?
At equilibrium, ΔG = 0. The relationship ΔG° = −RT ln K connects standard free energy change to equilibrium constant. ΔG°<0 → K>1; ΔG°>0 → K<1.
QWhat is the reaction quotient Q?
Q has the same form as Kc but uses current (non-equilibrium) concentrations. Comparing Q to Kc tells us the direction of spontaneous change.
QHow does Kc relate to reaction extent?
Kc > 10³ → essentially complete (products favoured). Kc < 10⁻³ → essentially no reaction. 10⁻³ to 10³ → significant amounts of both.
QWhat is the effect of inert gas at constant volume?
At constant volume, adding inert gas increases total pressure but not the partial pressures of reacting gases. Therefore, no equilibrium shift. At constant pressure, volume increases, so equilibrium shifts toward more moles of gas.

📋Syllabus & Learning Outcomes

According to PMDC/PMC MDCAT syllabus, Chemical Equilibrium covers:

📝Full Notes — Chemical Equilibrium

⚖️ Chemical Equilibrium – Schematic Notes

🔄 1. Chemical Equilibrium – Definition

  • State in a reversible reaction when the rate of forward reaction equals the rate of reverse reaction.
  • Reaction does not stop; concentrations of reactants and products remain constant (dynamic equilibrium).
  • Written with double arrow ⇌.
  • Can be approached from either direction.

👁️ 2. Macroscopic Characteristics

  • Closed system (no exchange of matter with surroundings).
  • Concentrations of reactants and products remain unchanged over time.
  • Temperature constant; no visible change, but molecular processes continue.
  • Equilibrium constant (Kc) has a fixed value at a given temperature, independent of initial concentrations.
  • Catalyst speeds up both forward and reverse reactions equally; does not change equilibrium composition or K, only reduces time to reach equilibrium.

⚖️ 3. Le Chatelier’s Principle

If a system at equilibrium is subjected to a change (stress), the system will shift in the direction that counteracts the imposed change.

  • Concentration change: Adding a reactant shifts equilibrium to the right (product side); removing a product shifts to the right. Adding product shifts to left.
  • Pressure change (gases only): Increasing pressure shifts to side with fewer moles of gas; decreasing pressure shifts to side with more moles.
    • If moles of gas equal on both sides, pressure has no effect on equilibrium position.
  • Temperature change:
    • Exothermic (ΔH = −ve): increase T → shifts to left (reactants); decrease T → shifts to right.
    • Endothermic (ΔH = +ve): increase T → shifts to right; decrease T → shifts to left.
  • Catalyst: No effect on equilibrium position; only helps attain equilibrium faster.
  • Inert gas addition at constant volume: no effect on equilibrium (partial pressures unchanged); at constant pressure: shifts if change in number of moles.

💧 4. Solubility Product (Ksp)

  • For a sparingly soluble salt, AmBn(s) ⇌ mAⁿ⁺ + nBᵐ⁻, Ksp = [Aⁿ⁺]ᵐ[Bᵐ⁻]ⁿ.
  • Ksp depends only on temperature.
  • If Qsp > Ksp → precipitation; Qsp < Ksp → no precipitate (unsaturated).
  • Lower Ksp means lower solubility (generally, for similar stoichiometry).

🧂 5. Common Ion Effect

  • When an ionic compound shares an ion with another compound already present, the solubility of the first decreases (Le Chatelier’s principle).
  • Example: Adding NaCl to a saturated solution of PbCl₂ reduces the solubility of PbCl₂ because of the common Cl⁻ ion.
  • Used in selective precipitation and in buffer preparation.

🧴 6. Buffer Solutions

  • Definition: Solutions that resist change in pH upon addition of small amounts of acid or base.
  • Types:
    • Acidic buffer: weak acid + its salt with strong base (e.g., CH₃COOH/CH₃COONa). pH < 7.
    • Basic buffer: weak base + its salt with strong acid (e.g., NH₄OH/NH₄Cl). pH > 7.
  • Buffer capacity depends on concentration of components and ratio (ideally 1:1). Maximum buffering when [HA] = [A⁻] (pH = pKₐ).
  • Blood buffering: H₂CO₃ / HCO₃⁻ maintains pH ~7.4.

🏭 7. Haber Process (Synthesis of Ammonia)

  • N₂(g) + 3 H₂(g) ⇌ 2 NH₃(g) ΔH = −92 kJ/mol (exothermic).
  • Conditions: High pressure (200–300 atm) – favours fewer moles (4 → 2); Moderate temperature (400–450°C) – compromise between rate and yield (low T favours equilibrium but slow); Iron catalyst (Fe with K₂O/Al₂O₃ promoters) increases rate without affecting equilibrium.
  • Unreacted gases are recycled. Liquification of NH₃ removes it, shifting equilibrium right.

🔑 High‑Yield MCQs & Traps

  • Dynamic equilibrium: rates equal, concentrations constant, not necessarily equal.
  • Kc only changes with temperature; catalysts do not change K.
  • Le Chatelier: temperature shift depends on ΔH; adding solid or pure liquid does not shift equilibrium.
  • For gaseous reactions, count moles of gas on each side to predict pressure effect.
  • Common ion effect decreases solubility (shift left).
  • Buffer: weak acid/base + its conjugate salt. Henderson‑Hasselbalch: pH = pKₐ + log([A⁻]/[HA]).
  • Haber process: high pressure, moderate temp, Fe catalyst, NH₃ removal shifts right.
  • ⚠️ Traps: "Catalyst increases yield of product at equilibrium" → False (only speeds up). "Adding inert gas at constant volume shifts equilibrium" → False. "Common ion increases solubility" → False (decreases). "Buffers keep pH neutral (7)" → False (maintain specific pH, not necessarily 7).

💡 MDCAT focus: Le Chatelier’s principle applications, Ksp and precipitation, buffer concepts, and Haber conditions.

✅Practice MCQs — Test 1

🧪 Basic Concepts

50 MCQs
1A chemical reaction is said to be in a state of dynamic equilibrium when:
  • A. The concentrations of reactants and products are equal.
  • B. The rate of the forward reaction equals the rate of the reverse reaction.
  • C. The reaction has completely stopped.
  • D. The mass of reactants equals the mass of products.
Answer: B
Dynamic equilibrium: equal rates.
2Which of the following is a macroscopic characteristic of a system at equilibrium?
  • A. It is achievable only from the reactant side.
  • B. The concentration of reactants continues to decrease slowly.
  • C. The measurable properties like density and color remain constant.
  • D. It can only occur in an open vessel.
Answer: C
Constant macroscopic properties at equilibrium.
3For a reversible reaction, if the value of the Equilibrium Constant (K_c) is very large, it indicates that:
  • A. The reaction is almost complete.
  • B. The reaction hardly proceeds forward.
  • C. Reactants are more stable than products.
  • D. Equilibrium is reached instantaneously.
Answer: A
Large K_c means products are highly favored.
4The units of K_c for the reaction H₂ + I₂ ⇌ 2HI are:
  • A. mol·dm⁻³
  • B. mol⁻²·dm⁶
  • C. No units
  • D. mol·dm³
Answer: C. No units
Δn = 0, so K_c is dimensionless.
5In a reversible reaction, catalysts are used to:
  • A. Increase the yield of the product.
  • B. Shift the equilibrium to the right.
  • C. Attain equilibrium in a shorter time.
  • D. Change the value of K_c.
Answer: C
Catalyst speeds up both forward and reverse reactions equally.
6The equilibrium constant for a reaction is K. The equilibrium constant for the reverse reaction will be:
  • A. K
  • B. -K
  • C. 1/K
  • D. √K
Answer: C. 1/K
Reverse reaction: K_rev = 1/K.
7Which statement is true regarding the "State of Equilibrium"?
  • A. It is independent of the initial concentrations of reactants.
  • B. It can only be reached in a closed system.
  • C. Forward and backward reactions occur at the same speed.
  • D. All of the above.
Answer: D
All statements are true for equilibrium.
8If the Reaction Quotient (Q_c) is less than K_c, the reaction will:
  • A. Proceed in the reverse direction.
  • B. Proceed in the forward direction.
  • C. Remain at equilibrium.
  • D. Stop immediately.
Answer: B
Q_c < K_c → forward reaction.
9For the reaction N₂O₄(g) ⇌ 2NO₂(g), the relationship between K_p and K_c is:
  • A. K_p = K_c
  • B. K_p = K_c(RT)¹
  • C. K_p = K_c(RT)⁻¹
  • D. K_p = K_c(RT)²
Answer: B
Δn = 1, K_p = K_c(RT).
10The value of K_c changes only with a change in:
  • A. Pressure
  • B. Concentration
  • C. Temperature
  • D. Volume
Answer: C. Temperature
K_c depends only on temperature.
11According to Le Chatelier’s Principle, if you increase the pressure on the system N₂ + 3H₂ ⇌ 2NH₃, the equilibrium will shift:
  • A. Toward the left (Reactants)
  • B. Toward the right (Products)
  • C. It will not shift
  • D. Toward the side with more moles of gas
Answer: B
Increase pressure → shift toward fewer moles.
12In an exothermic reaction, increasing the temperature will:
  • A. Increase the value of K_c.
  • B. Decrease the value of K_c.
  • C. Not affect K_c.
  • D. Shift the equilibrium to the right.
Answer: B. Decrease K_c
Exothermic: T↑ → K_c↓.
13Adding an inert gas at constant volume to an equilibrium mixture:
  • A. Shifts equilibrium toward more moles.
  • B. Shifts equilibrium toward fewer moles.
  • C. Has no effect on the equilibrium position.
  • D. Increases the yield of products.
Answer: C
Inert gas at constant V does not change partial pressures.
14For the reaction PCl₅ ⇌ PCl₃ + Cl₂, decreasing the volume of the container will:
  • A. Shift the equilibrium to the right.
  • B. Shift the equilibrium to the left.
  • C. Increase the value of K_c.
  • D. Decrease the rate of both reactions equally.
Answer: B
Decrease V → shift to fewer moles (left).
15Which of the following changes will shift the equilibrium 2SO₂ + O₂ ⇌ 2SO₃ (ΔH = -ve) to the right?
  • A. Increasing temperature
  • B. Decreasing pressure
  • C. Adding more O₂
  • D. Removing SO₂
Answer: C
Adding reactant shifts to right.
16In the reaction H₂(g) + I₂(g) ⇌ 2HI(g), the effect of increasing pressure is:
  • A. Increase in yield of HI.
  • B. Decrease in yield of HI.
  • C. No effect on equilibrium position.
  • D. Change in the value of K_p.
Answer: C
Δn = 0, pressure has no effect on position.
17If the temperature of an endothermic reaction is decreased, the equilibrium will shift toward:
  • A. The products.
  • B. The reactants.
  • C. Neither side.
  • D. The side with higher pressure.
Answer: B
Decrease T for endothermic → shift left (reactants).
18A catalyst affects the equilibrium by:
  • A. Lowering the activation energy for both forward and reverse reactions equally.
  • B. Changing the enthalpy of the reaction.
  • C. Increasing the concentration of products.
  • D. Shifting the equilibrium toward the endothermic side.
Answer: A
Catalyst lowers Ea for both directions equally.
19For the system Ice ⇌ Water, increasing the pressure will:
  • A. Shift the equilibrium toward ice.
  • B. Shift the equilibrium toward water.
  • C. Not affect the melting point.
  • D. Decrease the density of water.
Answer: B
Increase P favors liquid water (lower volume).
20When HCl gas is passed through a saturated solution of NaCl, NaCl precipitates due to:
  • A. Le Chatelier's Principle regarding pressure.
  • B. Common Ion Effect.
  • C. Increase in K_sp of NaCl.
  • D. Decrease in temperature.
Answer: B
Common ion (Cl⁻) decreases solubility.
21The Solubility Product (K_sp) of AgCl is expressed as:
  • A. [Ag⁺][Cl⁻]
  • B. [Ag⁺] + [Cl⁻]
  • C. [Ag⁺][Cl⁻] / [AgCl]
  • D. [Ag⁺]²[Cl⁻]
Answer: A
K_sp = [Ag⁺][Cl⁻].
22A solution is considered "unsaturated" if:
  • A. Ionic Product > K_sp
  • B. Ionic Product < K_sp
  • C. Ionic Product = K_sp
  • D. K_sp = 0
Answer: B
IP < K_sp → unsaturated.
23Precipitation of a salt occurs when its ionic product:
  • A. Equals its solubility product.
  • B. Is less than its solubility product.
  • C. Exceeds its solubility product.
  • D. Becomes constant.
Answer: C
IP > K_sp → precipitation.
24The solubility of PbCl₂ in water is 's' mol/dm³. Its K_sp is:
  • A. s²
  • B. 2s²
  • C. 4s²
  • D. 4s³
Answer: D
K_sp = [Pb²⁺][Cl⁻]² = s·(2s)² = 4s³.
25The Common Ion Effect is an application of:
  • A. Dalton's Law
  • B. Le Chatelier’s Principle
  • C. Graham's Law
  • D. Henry's Law
Answer: B
Common ion effect is explained by Le Chatelier’s principle.
26Which of the following will decrease the solubility of CaSO₄?
  • A. Adding NaCl
  • B. Adding Na₂SO₄
  • C. Adding water
  • D. Increasing the volume of the container
Answer: B
Common ion SO₄²⁻ reduces solubility.
27The Common Ion Effect is used in qualitative salt analysis for the precipitation of:
  • A. Group II radicals as sulfides.
  • B. Group III radicals as hydroxides.
  • C. Group IV radicals.
  • D. All of the above.
Answer: D
Common ion effect is used in all groups.
28If the K_sp of a salt A₂B is 4 × 10⁻¹², its solubility in mol·dm⁻³ is:
  • A. 1 × 10⁻⁴
  • B. 2 × 10⁻⁶
  • C. 1 × 10⁻⁶
  • D. 4 × 10⁻⁴
Answer: A
K_sp = 4s³ → s = (4×10⁻¹²/4)^(1/3) = 10⁻⁴.
29The addition of NH₄Cl to NH₄OH solution suppresses the ionization of NH₄OH due to:
  • A. Increase in pH.
  • B. Common Ion Effect (NH₄⁺).
  • C. Formation of a complex.
  • D. Decrease in temperature.
Answer: B
NH₄⁺ common ion suppresses base ionization.
30Which salt is more soluble in an acidic solution than in pure water?
  • A. AgCl
  • B. BaC₂O₄ (Barium Oxalate)
  • C. KNO₃
  • D. PbI₂
Answer: B
Oxalate is conjugate base of weak acid; H⁺ reacts with C₂O₄²⁻.
31A buffer solution is one which:
  • A. Has a pH of 7.
  • B. Resists changes in pH upon addition of small amounts of acid or base.
  • C. Is always made of a strong acid and strong base.
  • D. Changes color with pH.
Answer: B
Buffer resists pH change.
32An acidic buffer can be prepared by mixing:
  • A. CH₃COOH and CH₃COONa
  • B. HCl and NaCl
  • C. NH₄OH and NH₄Cl
  • D. NaOH and HCl
Answer: A
Weak acid + its salt.
33The pH of a basic buffer is calculated using the Henderson-Hasselbalch equation:
  • A. pH = pK_a + log [Salt]/[Acid]
  • B. pOH = pK_b + log [Salt]/[Base]
  • C. pH = 14 - pOH
  • D. Both B and C
Answer: D
Use pOH = pK_b + log(salt/base), then pH = 14 - pOH.
34The pH of human blood is maintained around 7.4 by which buffer system?
  • A. CH₃COOH / CH₃COONa
  • B. H₂CO₃ / HCO₃⁻
  • C. NH₄OH / NH₄Cl
  • D. HCl / NaCl
Answer: B. H₂CO₃ / HCO₃⁻
Bicarbonate buffer in blood.
35The capacity of a buffer is maximum when:
  • A. [Salt] = [Acid]
  • B. [Salt] > [Acid]
  • C. [Salt] < [Acid]
  • D. pH = 7
Answer: A
Maximum buffer capacity at [Salt] = [Acid] (pH = pK_a).
36When a small amount of HCl is added to an acetic acid buffer, the H⁺ ions are consumed by:
  • A. CH₃COOH
  • B. CH₃COO⁻ ions
  • C. Na⁺ ions
  • D. OH⁻ ions
Answer: B
CH₃COO⁻ + H⁺ → CH₃COOH.
37Which of the following is NOT a type of buffer?
  • A. HCN / NaCN
  • B. Na₂HPO₄ / NaH₂PO₄
  • C. NaCl / HCl
  • D. NH₃ / NH₄Cl
Answer: C
NaCl/HCl is not a buffer (strong acid + salt).
38If the pK_a of an acid is 4.74, the pH of an equimolar buffer of this acid and its salt will be:
  • A. 7.0
  • B. 4.74
  • C. 9.26
  • D. 5.74
Answer: B. 4.74
pH = pK_a when [salt] = [acid].
39Basic buffers usually have a pH:
  • A. Less than 7.
  • B. Greater than 7.
  • C. Equal to 7.
  • D. Equal to 0.
Answer: B. Greater than 7
Basic buffer pH > 7.
40The pOH of a buffer solution containing 0.1M NH₄OH and 0.1M NH₄Cl (K_b = 1.8 × 10⁻⁵) is:
  • A. 4.74
  • B. 9.26
  • C. 7.0
  • D. 5.0
Answer: A. 4.74
pOH = pK_b + log([salt]/[base]) = 4.74 + 0 = 4.74.
41The optimum temperature for the synthesis of ammonia by Haber’s process is approximately:
  • A. 200°C
  • B. 450°C
  • C. 800°C
  • D. 100°C
Answer: B. 450°C
Compromise temperature ~450°C.
42In Haber’s process, high pressure (200-300 atm) is used because:
  • A. The reaction is exothermic.
  • B. The reaction proceeds with a decrease in the number of moles.
  • C. The reaction is endothermic.
  • D. It prevents the catalyst from poisoning.
Answer: B
High pressure favors fewer moles.
43The catalyst used in Haber’s process is finely divided:
  • A. Copper
  • B. Iron with Al₂O₃/K₂O as promoters
  • C. Platinum
  • D. Nickel
Answer: B
Iron catalyst with promoters.
44The percentage yield of ammonia is increased by:
  • A. Increasing temperature.
  • B. Continuously removing ammonia as it is formed.
  • C. Decreasing pressure.
  • D. Adding an inert gas.
Answer: B
Removing product shifts equilibrium right.
45Haber’s process is an application of:
  • A. Le Chatelier’s Principle.
  • B. Boyle’s Law.
  • C. Graham’s Law.
  • D. Charle’s Law.
Answer: A
Optimized using Le Chatelier’s principle.
46What is the ratio of N₂ to H₂ by volume in Haber's process?
  • A. 1:1
  • B. 1:2
  • C. 1:3
  • D. 3:1
Answer: C. 1:3
Stoichiometric ratio 1:3.
47The reaction N₂ + 3H₂ ⇌ 2NH₃ is:
  • A. Endothermic
  • B. Exothermic
  • C. Reversible at high temperatures only
  • D. Irreversible in the presence of iron
Answer: B. Exothermic
ΔH = -92 kJ, exothermic.
48If the pressure in Haber's process is decreased, the rate of forward reaction will:
  • A. Increase
  • B. Decrease
  • C. Remain same
  • D. Become zero
Answer: B. Decrease
Fewer collisions, rate decreases.
49Promoters like K₂O and Al₂O₃ are added to the iron catalyst to:
  • A. Shift the equilibrium.
  • B. Increase the surface area and efficiency of the catalyst.
  • C. Change the ΔH of the reaction.
  • D. Decrease the cost of the process.
Answer: B
Promoters enhance catalyst performance.
50Which of the following conditions favors the maximum yield of NH₃?
  • A. High Temp, High Pressure
  • B. Low Temp, High Pressure
  • C. Low Temp, Low Pressure
  • D. High Temp, Low Pressure
Answer: B
Exothermic: low T; fewer moles: high P.

✅Practice MCQs — Test 2

🧪 Advanced Concepts

50 MCQs
1For the reaction A + B ⇌ C + D, if the initial concentrations of A and B are 1 M each, and at equilibrium the concentration of D is x M, the value of K_c is:
  • A. x²/(1-x)
  • B. x²/(1-x)²
  • C. x²/(1-2x)²
  • D. x²/(1-x/2)
Answer: B. x²/(1-x)²
K_c = [C][D]/[A][B] = x²/(1-x)².
2The relationship ΔG° = -RT ln K_c suggests that if ΔG° is negative, then:
  • A. K_c < 1 and reactants are favored.
  • B. K_c > 1 and products are favored.
  • C. K_c = 0.
  • D. The reaction is at equilibrium initially.
Answer: B
Negative ΔG° → K > 1.
3For the reaction PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), the degree of dissociation (α) is related to K_p and total pressure (P) by:
  • A. α = √(K_p/(K_p + P))
  • B. α = K_p/P
  • C. α = √(P/(K_p + P))
  • D. α = √(K_p·P)
Answer: A
K_p = α²P/(1-α²) → α derived as shown.
4If the equilibrium constant for N₂ + O₂ ⇌ 2NO is K₁ and for NO ⇌ ½N₂ + ½O₂ is K₂, then:
  • A. K₁ = 1/K₂
  • B. K₁ = (K₂)²
  • C. K₂ = 1/√K₁
  • D. K₂ = √K₁
Answer: C
Reverse and half coefficients: K₂ = 1/√K₁.
5In which of the following equilibrium systems will the numerical value of K_p be equal to K_c?
  • A. N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
  • B. PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)
  • C. H₂(g) + I₂(g) ⇌ 2HI(g)
  • D. 2SO₂(g) + O₂(g) ⇌ 2SO₃(g)
Answer: C
Δn = 0 → K_p = K_c.
6The units for K_p in the reaction 2NO₂(g) ⇌ N₂O₄(g) are:
  • A. atm
  • B. atm⁻¹
  • C. atm⁻²
  • D. Unitless
Answer: B. atm⁻¹
Δn = -1 → K_p has units atm⁻¹.
7At a given temperature, K_c for 2HI ⇌ H₂ + I₂ is 0.02. If the reaction is started with 2 M of HI, the concentration of H₂ at equilibrium will be:
  • A. 0.22 M
  • B. 0.44 M
  • C. 0.02 M
  • D. 0.80 M
Answer: A. 0.22 M
ICE table yields [H₂] ≈ 0.22 M.
8The Van't Hoff equation ln(K₂/K₁) = (ΔH°/R)(1/T₁ - 1/T₂) implies that for an endothermic reaction, a plot of ln K vs 1/T has:
  • A. A positive slope.
  • B. A negative slope.
  • C. Zero slope.
  • D. A parabolic curve.
Answer: B. Negative slope
Endothermic ΔH° > 0, slope = -ΔH°/R → negative slope.
9If the volume of the container is doubled for the system N₂O₄(g) ⇌ 2NO₂(g), the value of K_c will:
  • A. Double.
  • B. Be halved.
  • C. Remain unchanged.
  • D. Quadruple.
Answer: C
K_c is constant at constant T.
10A reaction reaches equilibrium when the "Chemical Potential" (μ) of the reactants is ______ the chemical potential of the products.
  • A. Greater than
  • B. Less than
  • C. Equal to
  • D. Twice
Answer: C. Equal to
Equilibrium: μ_reactants = μ_products.
11In the equilibrium C(s) + H₂O(g) ⇌ CO(g) + H₂(g), adding more solid carbon at constant temperature and volume will:
  • A. Shift equilibrium to the right.
  • B. Shift equilibrium to the left.
  • C. Have no effect on the equilibrium position.
  • D. Increase the pressure of CO.
Answer: C
Solids don't affect equilibrium position.
12Adding an inert gas (He) to the system PCl₅ ⇌ PCl₃ + Cl₂ at constant pressure will:
  • A. Shift equilibrium to the left.
  • B. Shift equilibrium to the right.
  • C. Have no effect.
  • D. Increase the partial pressure of PCl₅.
Answer: B
Adding inert gas at constant P → volume increases → shift to more moles (right).
13For the reaction 2A(g) + B(g) ⇌ 3C(g) + D(g), the addition of a catalyst will increase the rate of the forward reaction by 25%. The rate of the reverse reaction will increase by:
  • A. 12.5%
  • B. 25%
  • C. 50%
  • D. 0%
Answer: B. 25%
Catalyst accelerates both directions equally.
14In the synthesis of SO₃ (2SO₂ + O₂ ⇌ 2SO₃ + Heat), the "Physical State" of the system that maximizes yield is:
  • A. Low Temp, Low Pressure
  • B. High Temp, High Pressure
  • C. Low Temp, High Pressure
  • D. High Temp, Low Pressure
Answer: C
Exothermic → low T; fewer moles → high P.
15For a reaction where Δn = 0, an increase in pressure will:
  • A. Increase the yield.
  • B. Decrease the yield.
  • C. Not change the equilibrium position but increase the rate of reaching it.
  • D. Change the value of K_p.
Answer: C
No shift, but rate increases due to higher concentrations.
16If the temperature of an exothermic reaction is increased by 10 K, the K_c value typically:
  • A. Increases.
  • B. Decreases.
  • C. Remains constant.
  • D. Becomes zero.
Answer: B. Decreases
Exothermic: T↑ → K_c↓.
17Which of the following will change the value of K_p for the Haber process?
  • A. Adding more N₂.
  • B. Increasing the total pressure.
  • C. Changing the temperature from 400°C to 500°C.
  • D. Using a more efficient Iron catalyst.
Answer: C
Only temperature changes K_p.
18In the decomposition of Calcium Carbonate (CaCO₃(s) ⇌ CaO(s) + CO₂(g)), the equilibrium constant K_p is equal to:
  • A. P_CO₂
  • B. P_CO₂ · P_CaO / P_CaCO₃
  • C. 1 / P_CO₂
  • D. P_CO₂ + P_CaO
Answer: A. P_CO₂
Solids have activity = 1; K_p = P_CO₂.
19For the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g), the units of K_c are:
  • A. mol⁻²·dm⁶
  • B. mol²·dm⁻⁶
  • C. mol·dm⁻³
  • D. dm³·mol⁻¹
Answer: A
K_c = [NH₃]²/[N₂][H₂]³ → units mol⁻²·dm⁶.
20Le Chatelier’s principle is not applicable to:
  • A. H₂ + I₂ ⇌ 2HI
  • B. Fe(s) + S(s) ⇌ FeS(s) (Pure solids only)
  • C. N₂ + 3H₂ ⇌ 2NH₃
  • D. PCl₅ ⇌ PCl₃ + Cl₂
Answer: B
Only solids, no gaseous/aqueous species to shift.
21The solubility of A₂B₃ is 's' mol/dm³. Its Solubility Product (K_sp) is given by:
  • A. 6s⁵
  • B. 36s⁵
  • C. 108s⁵
  • D. 108s⁴
Answer: C. 108s⁵
K_sp = (2s)²(3s)³ = 108s⁵.
22If the K_sp of AgCl is 1 × 10⁻¹⁰, its solubility in 0.1 M NaCl solution will be:
  • A. 1 × 10⁻⁵ M
  • B. 1 × 10⁻⁹ M
  • C. 1 × 10⁻¹⁰ M
  • D. 1 × 10⁻¹¹ M
Answer: B. 1 × 10⁻⁹ M
s = K_sp/[Cl⁻] = 10⁻¹⁰/0.1 = 10⁻⁹.
23Which of the following will have the lowest solubility in water if their K_sp values are all 1 × 10⁻¹²?
  • A. AB type salt
  • B. A₂B type salt
  • C. AB₃ type salt
  • D. A₃B₂ type salt
Answer: D. A₃B₂ type salt
A₃B₂: K_sp = 108s⁵ → s lowest for given K_sp.
24In the fractional precipitation of Cl⁻ and I⁻ by AgNO₃, which will precipitate first? (K_sp of AgCl = 1.8 × 10⁻¹⁰, AgI = 8.5 × 10⁻¹⁷)
  • A. AgCl
  • B. AgI
  • C. Both simultaneously
  • D. Neither
Answer: B. AgI
Lower K_sp precipitates first.
25The solubility of Mg(OH)₂ (K_sp = 1.2 × 10⁻¹¹) in a buffer solution of pH = 12 is:
  • A. 1.2 × 10⁻⁵ M
  • B. 1.2 × 10⁻⁷ M
  • C. 1.2 × 10⁻⁹ M
  • D. 1.2 × 10⁻² M
Answer: B. 1.2 × 10⁻⁷ M
pH 12 → [OH⁻] = 0.01; s = K_sp/[OH⁻]² = 1.2×10⁻⁷.
26The Common Ion Effect is responsible for the ______ of a weak electrolyte in the presence of a strong electrolyte having a common ion.
  • A. Increased ionization
  • B. Decreased ionization
  • C. Complete neutralization
  • D. Sublimation
Answer: B
Common ion suppresses ionization.
27For a salt M₂X, if the solubility is doubled, the K_sp will increase by a factor of:
  • A. 2
  • B. 4
  • C. 8
  • D. 16
Answer: C. 8
K_sp ∝ (2s)²(s) = 4s³; doubling s → factor 8.
28In Group II of qualitative analysis, H₂S is passed in the presence of HCl to:
  • A. Increase [S²⁻]
  • B. Decrease [S²⁻] via Common Ion Effect
  • C. Increase the solubility of Group IV radicals
  • D. Oxidize the radicals
Answer: B
HCl suppresses S²⁻ concentration.
29The K_sp of CaF₂ is 4 × 10⁻¹¹. The concentration of F⁻ ions in a saturated solution is:
  • A. 2 × 10⁻⁴ M
  • B. 4 × 10⁻⁴ M
  • C. 3.1 × 10⁻⁴ M
  • D. 1 × 10⁻⁴ M
Answer: B. 4 × 10⁻⁴ M
s = ∛(K_sp/4) = 2.15×10⁻⁴; [F⁻] = 2s = 4.3×10⁻⁴ ≈ 4×10⁻⁴.
30When NH₄Cl is added to NH₄OH, the OH⁻ concentration:
  • A. Increases.
  • B. Decreases.
  • C. Remains the same.
  • D. Becomes zero.
Answer: B. Decreases
Common ion NH₄⁺ reduces OH⁻.
31The "Buffer Capacity" is defined as the number of moles of acid or base added to 1 liter of buffer to change its pH by:
  • A. 7 units
  • B. 1 unit
  • C. 0.1 unit
  • D. 14 units
Answer: B. 1 unit
Buffer capacity: pH change by 1 unit.
32A buffer solution contains 0.1 M Weak Acid (pK_a = 5.0) and 0.01 M of its conjugate salt. The pH is:
  • A. 5.0
  • B. 4.0
  • C. 6.0
  • D. 7.0
Answer: B. 4.0
pH = 5.0 + log(0.01/0.1) = 4.0.
33Which mixture acts as a "Universal Buffer" in the physiological range?
  • A. HCl / NaCl
  • B. H₂PO₄⁻ / HPO₄²⁻
  • C. NaOH / NH₄Cl
  • D. CH₃COOH / HCl
Answer: B. H₂PO₄⁻ / HPO₄²⁻
Phosphate buffer is universal physiological buffer.
34The pH of a buffer solution is independent of ______ but depends on the ______ of the components.
  • A. Temperature; Color
  • B. Total Volume; Ratio of concentrations
  • C. Concentration; Catalyst
  • D. pK_a; Pressure
Answer: B
Henderson-Hasselbalch: pH depends on ratio, not total volume.
35For an acidic buffer, if [Salt] = 10 × [Acid], then:
  • A. pH = pK_a
  • B. pH = pK_a + 1
  • C. pH = pK_a - 1
  • D. pH = 14 - pK_a
Answer: B. pH = pK_a + 1
log(10) = 1, so pH = pK_a + 1.
36What happens to the pH of a CH₃COOH / CH₃COONa buffer if it is diluted 10 times?
  • A. Increases by 1.
  • B. Decreases by 1.
  • C. Remains practically unchanged.
  • D. Becomes 7.
Answer: C
Ratio stays same, pH unchanged.
37In the Henderson-Hasselbalch equation, if the ratio of [Salt]/[Acid] is inverted, the pH changes by:
  • A. 2 log([Salt]/[Acid])
  • B. No change.
  • C. pK_a
  • D. 14 - pH
Answer: A
Inverting ratio changes pH by 2×log of the original ratio.
38The pK_a of HCN is 9.2. A buffer of HCN and NaCN will be most effective at pH:
  • A. 7.0
  • B. 9.2
  • C. 4.8
  • D. 1.0
Answer: B. 9.2
Maximum buffer capacity at pH = pK_a.
39Adding 0.01 moles of NaOH to a buffer containing 0.1 M each of HA and A⁻ will result in:
  • A. [HA] becoming 0.11 and [A⁻] becoming 0.09.
  • B. [HA] becoming 0.09 and [A⁻] becoming 0.11.
  • C. [HA] becoming 0.1 and [A⁻] becoming 0.11.
  • D. No change in concentrations.
Answer: B
NaOH converts HA to A⁻: HA decreases, A⁻ increases.
40The enthalpy of formation (ΔH_f) of NH₃ is -46.1 kJ/mol. For the Haber reaction N₂ + 3H₂ ⇌ 2NH₃, the total ΔH is:
  • A. -46.1 kJ
  • B. -92.2 kJ
  • C. +92.2 kJ
  • D. -23.05 kJ
Answer: B. -92.2 kJ
For 2 moles, ΔH = 2 × -46.1 = -92.2 kJ.
41In the Haber process, why is a temperature of 450°C used despite the reaction being exothermic?
  • A. To shift the equilibrium to the right.
  • B. To provide a "Compromise Temperature" for an acceptable rate and yield.
  • C. To vaporize the catalyst.
  • D. To decrease the activation energy of the reverse reaction.
Answer: B
Compromise temperature balances rate and yield.
42If the pressure in the Haber process is increased from 200 atm to 400 atm, the K_p value will:
  • A. Double.
  • B. Quadruple.
  • C. Remain constant.
  • D. Be halved.
Answer: C. Remain constant
K_p depends only on temperature.
43The function of Al₂O₃ in the Haber catalyst is to:
  • A. Act as the primary catalyst.
  • B. Prevent the "Sintering" (clumping) of Iron particles.
  • C. Absorb moisture.
  • D. Shift equilibrium toward ammonia.
Answer: B
Al₂O₃ prevents sintering.
44Which of the following is a "Kinetic" factor in the Haber process?
  • A. High Pressure.
  • B. Low Temperature.
  • C. Use of a Catalyst.
  • D. Removal of NH₃.
Answer: C
Catalyst affects rate (kinetics).
45What is the partial pressure of N₂ at equilibrium if the total pressure is P and N₂, H₂, NH₃ are in 1:3:2 molar ratio?
  • A. P/6
  • B. P/3
  • C. P/2
  • D. P/4
Answer: A. P/6
Total moles = 6; mole fraction N₂ = 1/6 → partial pressure P/6.
46The Haber process was revolutionary because it allowed the "Fixation" of atmospheric nitrogen into:
  • A. Nitric acid.
  • B. Fertilizers and explosives.
  • C. Plastics.
  • D. Noble gases.
Answer: B. Fertilizers and explosives
NH₃ → fertilizers.
47In the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g), if Δn is -2, then K_p is related to K_c by:
  • A. K_p = K_c(RT)²
  • B. K_p = K_c(RT)⁻²
  • C. K_p = K_c / RT
  • D. K_p = K_c
Answer: B
K_p = K_c(RT)^{-2}.
48Le Chatelier's principle predicts that the yield of NH₃ will decrease if:
  • A. Temperature is lowered.
  • B. H₂ is added.
  • C. Volume of the vessel is increased.
  • D. NH₃ is removed as a liquid.
Answer: C
Increase volume → expansion → shift to more moles (left).
49The efficiency of the Haber process catalyst is poisoned by the presence of trace amounts of:
  • A. K₂O
  • B. CO or H₂S
  • C. Al₂O₃
  • D. Rare earth metals
Answer: B. CO or H₂S
CO and H₂S poison iron catalyst.
50For the equilibrium N₂ + 3H₂ ⇌ 2NH₃, if all species are 1 M at equilibrium, the value of K_c is:
  • A. 1
  • B. 1
  • C. 4
  • D. 0.25
Answer: B. 1
K_c = [NH₃]²/([N₂][H₂]³) = 1²/(1·1³) = 1.

✅Practice MCQs — Test 3

🧪 Exam-Level Questions

50 MCQs
1For a reaction in a non-ideal gas phase, the true equilibrium constant (K) is expressed using "Fugacity" (f). The relationship between the standard K and the pressure-based K_p is K = K_p · K_γ. If the fugacity coefficient (γ) increases with pressure, the yield of products will:
  • A. Increase more than predicted by the Ideal Gas Law.
  • B. Decrease compared to the ideal prediction.
  • C. Remain exactly as K_p predicts.
  • D. Become independent of temperature.
Answer: B
Non-ideality can reduce product yield.
2In the derivation of the "Reaction Isotherm," ΔG = ΔG° + RT ln Q. At the point where the reaction coordinate (ξ) reaches its minimum Gibbs energy, which of the following is mathematically mandatory?
  • A. Q = 0
  • B. (∂G/∂ξ)_{T,P} = 0
  • C. ΔG° = 0
  • D. T = 0 K
Answer: B
Equilibrium condition: derivative of G w.r.t ξ is zero.
3For the dissociation of a gas A₂ ⇌ 2A, if the degree of dissociation is α, the total number of moles at equilibrium starting from 1 mole of A₂ is 1 + α. The partial pressure of A in terms of total pressure P is:
  • A. αP/(1+α)
  • B. 2αP/(1+α)
  • C. α²P/(1-α)
  • D. (1-α)P/(1+α)
Answer: B
Moles A = 2α; mole fraction = 2α/(1+α); p_A = (2αP)/(1+α).
4The "Van’t Hoff Isochore" equation d(ln K_p)/dT = ΔH°/RT² implies that for a reaction with ΔH° = 0, the equilibrium constant:
  • A. Is infinitely large.
  • B. Is zero.
  • C. Is independent of temperature.
  • D. Changes exponentially with pressure.
Answer: C
ΔH°=0 → K independent of T.
5In a system where 2A(g) ⇌ B(g) + C(s), the equilibrium constant K_p is determined to be 0.5 atm⁻¹. If the total pressure is halved, the mole fraction of B at equilibrium will:
  • A. Increase.
  • B. Decrease.
  • C. Remain unchanged.
  • D. Become equal to the mole fraction of C.
Answer: B
Halving P shifts equilibrium to more moles (right) → B increases.
6The "Principle of Least Restraint" (Le Chatelier) can be derived from the Second Law of Thermodynamics. It states that any external stress on a system at equilibrium will:
  • A. Increase the entropy of the universe.
  • B. Decrease the internal energy to zero.
  • C. Shift the system to minimize the chemical potential gradient.
  • D. Both A and C.
Answer: D
Both entropy consideration and minimizing chemical potential gradient.
7For the reaction N₂O₄ ⇌ 2NO₂, the slope of the plot of log K_p vs 1/T is -2991. Calculate the enthalpy of reaction (ΔH°) in kJ/mol (Given R = 8.314 J/mol·K):
  • A. +57.2 kJ/mol
  • B. -57.2 kJ/mol
  • C. +24.8 kJ/mol
  • D. +114.4 kJ/mol
Answer: A. +57.2 kJ/mol
Slope = -ΔH°/(2.303R) → ΔH° = -2.303×8.314×(-2991) ≈ 57.2 kJ/mol.
8If a reaction has a K_c value of 1 × 10³⁰ at 25°C, the reaction is essentially:
  • A. Non-spontaneous.
  • B. In equilibrium with equal concentrations.
  • C. Quantitative (goes to completion).
  • D. Explosive.
Answer: C
Huge K → essentially complete.
9In a rigid container of constant volume, adding an inert gas at constant temperature to the equilibrium 2SO₂ + O₂ ⇌ 2SO₃ results in:
  • A. An increase in the partial pressure of SO₃.
  • B. A decrease in the total pressure.
  • C. No change in the partial pressures of the reactants or products.
  • D. A shift toward the reactants.
Answer: C
Constant volume → partial pressures unchanged.
10The "Degree of Freedom" (F) for the equilibrium NH₄Cl(s) ⇌ NH₃(g) + HCl(g) when starting with pure NH₄Cl is:
  • A. 0
  • B. 1
  • C. 2
  • D. 3
Answer: B. 1
F = C - P + 2 = 1 - 2 + 2 = 1.
11The "Debye-Hückel Limiting Law" states that the activity coefficient (γ) of an ion decreases as "Ionic Strength" (μ) increases. This means that adding KNO₃ (non-common ion) to a saturated solution of AgCl will:
  • A. Decrease the solubility of AgCl.
  • B. Increase the solubility of AgCl (Salt Effect).
  • C. Have no effect on AgCl.
  • D. Precipitate AgNO₃.
Answer: B
Increased ionic strength reduces activity coefficients, increasing solubility.
12Calculate the Ionic Strength (μ) of a 0.1 M Na₂SO₄ solution:
  • A. 0.1
  • B. 0.2
  • C. 0.3
  • D. 0.6
Answer: C. 0.3
μ = 0.5(2×0.1×1² + 0.1×2²) = 0.5(0.2+0.4)=0.3.
13For a sparingly soluble salt M_pX_q, the relation between solubility (s) and K_sp is K_sp = p^p q^q s^{(p+q)}. What is the K_sp expression for Zirconium Phosphate Zr₃(PO₄)₄?
  • A. 108s⁷
  • B. 6912s⁷
  • C. 144s⁷
  • D. 432s⁷
Answer: B. 6912s⁷
K_sp = 3³·4⁴·s⁷ = 27·256·s⁷ = 6912s⁷.
14In the presence of a "Complexing Agent" like NH₃, the solubility of AgCl increases because:
  • A. The K_sp of AgCl changes.
  • B. The concentration of free Ag⁺ ions is reduced by the formation of [Ag(NH₃)₂]⁺.
  • C. NH₃ acts as a catalyst for dissolution.
  • D. AgCl reacts with Cl⁻ to form AgCl₂⁻.
Answer: B
Complexation reduces free Ag⁺, dissolution shifts forward.
15The "Simultaneous Solubility" of two salts with a common ion (e.g., AgCl and AgBr) results in a concentration of the common ion (Ag⁺) that is:
  • A. Equal to the sum of the solubilities of both salts.
  • B. Determined by the salt with the larger K_sp only.
  • C. Determined by the relation [Ag⁺] = √(K_sp1 + K_sp2).
  • D. Zero.
Answer: C
Simultaneous equilibrium: [Ag⁺] satisfies both K_sp.
16At the "Isoelectric Point" of an amino acid, its solubility is usually:
  • A. Maximum.
  • B. Minimum.
  • C. Infinite.
  • D. Independent of pH.
Answer: B. Minimum
At pI, net charge zero → least soluble.
17If the K_sp of Mg(OH)₂ is 1.2 × 10⁻¹¹, at what pH will precipitation begin from a 0.01 M Mg²⁺ solution?
  • A. 4.5
  • B. 9.5
  • C. 10.5
  • D. 12.0
Answer: B. 9.5
[OH⁻] = √(K_sp/[Mg²⁺]) = √(1.2×10⁻¹¹/0.01)=3.46×10⁻⁵; pOH=4.46; pH=9.54≈9.5.
18The "Common Ion Effect" can be mathematically viewed as a shift in equilibrium that maintains the constant value of:
  • A. The Reaction Quotient.
  • B. The Ion Product.
  • C. The Solubility Product (K_sp), assuming activity coefficients are near unity.
  • D. The pH.
Answer: C
Equilibrium shifts to maintain constant K_sp.
19What is the solubility of CaF₂ (K_sp = 4 × 10⁻¹¹) in a solution containing 0.01 M NaF?
  • A. 4 × 10⁻⁷ M
  • B. 4 × 10⁻⁹ M
  • C. 2 × 10⁻⁵ M
  • D. 1 × 10⁻⁴ M
Answer: A. 4 × 10⁻⁷ M
s = K_sp/(0.01)² = 4×10⁻⁷ M.
20Which of the following sulfides has the lowest K_sp and precipitates even in the presence of high H⁺ concentration (Group II)?
  • A. ZnS
  • B. MnS
  • C. CuS
  • D. FeS
Answer: C. CuS
CuS has very low K_sp, precipitates in acidic conditions.
21The "Buffer Index" (β) is mathematically defined as β = db/dpH. For a weak acid buffer, β is proportional to:
  • A. 1/([Salt] + [Acid])
  • B. [HA][A⁻]/([HA] + [A⁻])
  • C. The total volume.
  • D. The square root of K_a.
Answer: B
β ∝ [HA][A⁻]/([HA]+[A⁻]).
22A buffer solution is prepared using a weak acid with pK_a = 4.76. At what pH will the buffer capacity be exactly 50% of its maximum value?
  • A. 4.76
  • B. 3.76 or 5.76 (approximate range)
  • C. 4.76 ± 0.52
  • D. 7.00
Answer: C
Half-max capacity roughly ±0.5 units from pK_a.
23In "Polyprotic Buffer Systems" (like Phosphoric acid), the pH of a solution containing equal parts NaH₂PO₄ and Na₂HPO₄ is governed by:
  • A. pK_a1
  • B. pK_a2
  • C. pK_a3
  • D. The average of pK_a1 and pK_a2
Answer: B. pK_a2
pK_a2 for H₂PO₄⁻/HPO₄²⁻.
24When a buffer is diluted by a factor of 100, the "Buffer Capacity" (β):
  • A. Increases 100 times.
  • B. Decreases 100 times.
  • C. Remains unchanged.
  • D. Becomes zero.
Answer: B. Decreases 100 times
Buffer capacity is proportional to total concentration; dilution reduces β.
25The pH of an "Amphiprotic" salt solution like NaHCO₃ is calculated as:
  • A. pH = pK_a + log [Salt]/[Acid]
  • B. pH = ½(pK_a1 + pK_a2)
  • C. pH = 7 + ½pK_a + ½log C
  • D. pH = -log √K_w
Answer: B
For amphiprotic species, pH ≈ (pK_a1 + pK_a2)/2.
26Which of the following effects explains why the pH of a buffer changes slightly when a neutral salt like NaCl is added?
  • A. Common Ion Effect.
  • B. The "Ionic Strength Effect" on activity coefficients.
  • C. Hydrolysis of NaCl.
  • D. Oxidation of the buffer.
Answer: B
Ionic strength alters activity coefficients, shifting effective pH.
27For the titration of a weak acid with a strong base, the pH at the "Half-Equivalence Point" is exactly:
  • A. 7.0
  • B. pK_a
  • C. 14 - pK_b
  • D. pK_w
Answer: B. pK_a
Half-neutralization: [HA]=[A⁻] → pH = pK_a.
28The "Van Slyke Equation" for buffer capacity indicates that β is maximized when the concentration of the acid equals the concentration of its conjugate base. This occurs when:
  • A. pH = 7
  • B. pH = pK_a
  • C. pH = pK_b
  • D. [H⁺] = 10⁻⁷
Answer: B. pH = pK_a
Max β at pH = pK_a.
29Blood pH (7.4) is slightly higher than the pK_a of the bicarbonate system (6.1). This implies that in human blood:
  • A. [H₂CO₃] > [HCO₃⁻]
  • B. [HCO₃⁻] ≈ 20 × [H₂CO₃]
  • C. The buffer is at its maximum capacity.
  • D. The pH is controlled by HCl.
Answer: B
pH = pK_a + log([HCO₃⁻]/[H₂CO₃]) → ratio ≈ 20.
30What is the pH of a solution formed by mixing 50 mL of 0.1 M NH₃ and 25 mL of 0.1 M HCl (pK_b of NH₃ = 4.74)?
  • A. 4.74
  • B. 9.26
  • C. 7.0
  • D. 8.26
Answer: B. 9.26
Forms buffer: [NH₄⁺]=0.1×25/75=0.0333, [NH₃]=(0.1×50-0.1×25)/75=0.0333; pOH=pK_b+log(0.0333/0.0333)=4.74; pH=9.26.
31In the Haber process, the "Rate-Determining Step" (RDS) on the iron catalyst surface is generally considered to be:
  • A. The adsorption of H₂.
  • B. The dissociation of the N≡N triple bond (N₂ adsorption).
  • C. The desorption of NH₃.
  • D. The diffusion of H atoms.
Answer: B
N₂ dissociation is slow (high bond energy).
32The "Langmuir-Hinshelwood Mechanism" for the Haber process implies that the reaction occurs between:
  • A. A gas-phase N₂ molecule and adsorbed H atoms.
  • B. Adsorbed N atoms and adsorbed H atoms.
  • C. Two gas-phase molecules colliding near the surface.
  • D. NH₃ and the catalyst pores.
Answer: B
Both reactants adsorbed and react on surface.
33The "Temkin-Pyzhev Isotherm" is specifically used to describe the kinetics of the Haber process by accounting for:
  • A. The non-uniformity of the catalyst surface.
  • B. The increase in pressure.
  • C. The cooling of the reactor.
  • D. The purity of the nitrogen gas.
Answer: A
Accounts for surface heterogeneity.
34Why is the "Recirculation Loop" essential in industrial Haber plants?
  • A. To increase the temperature.
  • B. To achieve nearly 100% conversion by recycling unreacted N₂ and H₂ after removing NH₃.
  • C. To cool the catalyst.
  • D. To add more catalyst mid-reaction.
Answer: B
Recycling increases overall conversion.
35"Catalyst Sintering" in the Haber process refers to:
  • A. The poisoning of the catalyst by CO.
  • B. The loss of active surface area due to the fusion of small iron particles at high temperatures.
  • C. The evaporation of iron.
  • D. The reaction of iron with nitrogen to form nitrides.
Answer: B
Sintering reduces surface area.
36The use of "Promoters" like K₂O works by:
  • A. Increasing the surface area of the iron.
  • B. Lowering the "Work Function" of the iron, facilitating electron transfer to the π* orbitals of N₂.
  • C. Absorbing heat.
  • D. Increasing the pressure.
Answer: B
K₂O promotes N₂ dissociation by electron donation.
37The Haber process is "Autothermal" in some modern designs, meaning:
  • A. It requires no electricity.
  • B. The heat released by the exothermic reaction is used to maintain the incoming gas temperature.
  • C. It uses solar energy.
  • D. The reaction stops itself.
Answer: B
Self-sustaining heat balance.
38If the "Fugacity" of H₂ is lower than its partial pressure under high-pressure conditions, the actual yield of NH₃ will be ______ than the ideal yield.
  • A. Higher
  • B. Lower
  • C. Exactly the same
  • D. Zero
Answer: B
Lower fugacity means effective pressure lower, yield decreases.
39The equilibrium N₂ + 3H₂ ⇌ 2NH₃ shows that the volume of the system at constant pressure will ______ as the reaction proceeds.
  • A. Increase
  • B. Decrease
  • C. Remain constant
  • D. Oscillate
Answer: B. Decrease
Fewer moles → volume decreases.
40Which thermodynamic property of the Haber process makes it impossible to achieve high yields at high temperatures?
  • A. ΔS is positive.
  • B. ΔH is negative (Exothermic).
  • C. Activation energy is zero.
  • D. Iron is a solid.
Answer: B
Exothermic: high T shifts equilibrium to reactants.
41In the gaseous equilibrium A ⇌ B (K₁) and B ⇌ C (K₂), the equilibrium constant for A ⇌ C is:
  • A. K₁ + K₂
  • B. K₁ × K₂
  • C. K₁ / K₂
  • D. (K₁ × K₂)^{1/2}
Answer: B. K₁ × K₂
Multiply equilibrium constants.
42A system contains 0.1 M HA (K_a = 10⁻⁵) and 0.1 M HB (K_a = 10⁻⁷). The concentration of H⁺ is approximately:
  • A. 10⁻⁶ M
  • B. 10⁻³ M
  • C. 10⁻⁵ M
  • D. 1.1 × 10⁻³ M
Answer: D
HA dominates H⁺; [H⁺] ≈ √(0.1×10⁻⁵) = 10⁻³; plus minor from HB, total ~1.1×10⁻³.
43The "Reaction Quotient" Q for the reaction N₂O₄ ⇌ 2NO₂ is 5.0. If K_c = 0.5, in which direction is the reaction "spontaneously" moving?
  • A. Forward.
  • B. Backward (Toward N₂O₄).
  • C. It is at equilibrium.
  • D. Spontaneity cannot be determined from Q.
Answer: B
Q > K → reaction goes backward.
44What is the pH of a 10⁻⁸ M HCl solution?
  • A. 8.0
  • B. 7.0
  • C. 6.98 (due to water's contribution)
  • D. 1.0
Answer: C. 6.98
Very dilute acid, water autoionization considered → pH ≈ 6.98.
45"Le Chatelier’s Principle" fails to predict the shift in equilibrium if:
  • A. The temperature is changed.
  • B. Multiple parameters (P, T, V) are changed simultaneously in opposing ways.
  • C. A catalyst is added.
  • D. The reaction is reversible.
Answer: B
Simultaneous changes can have opposing effects.
46In the reaction I₂(g) ⇌ 2I(g), the degree of dissociation α increases as:
  • A. Pressure increases.
  • B. Volume decreases.
  • C. Temperature increases (assuming endothermic dissociation).
  • D. I₂ is added.
Answer: C
Endothermic dissociation: increasing T increases α.
47The equilibrium constant for the water-gas shift reaction CO + H₂O ⇌ CO₂ + H₂ is 1.0 at 1100 K. If the initial concentrations are all 0.1 M, the equilibrium concentrations will be:
  • A. All 0.1 M
  • B. 0.2 M for products
  • C. Higher for reactants
  • D. Zero
Answer: A. All 0.1 M
K = 1, equal concentrations; remains 0.1 M each.
48Which of the following is a "State Function" that is zero for a system at equilibrium?
  • A. H
  • B. S
  • C. G
  • D. ΔG (at constant T, P)
Answer: D
At equilibrium, ΔG = 0.
49In a saturated solution of Ca₃(PO₄)₂, if the concentration of Ca²⁺ is x, the K_sp is:
  • A. x⁵
  • B. 108x⁵
  • C. x³(2x/3)²
  • D. (x/3)³ · (x/2)²
Answer: C
From stoichiometry, [PO₄³⁻] = 2x/3; K_sp = x³(2x/3)².
50The "Thermodynamic Equilibrium Constant" is always:
  • A. Dependent on pressure.
  • B. Dimensionless.
  • C. Equal to K_c.
  • D. Larger than 1.
Answer: B. Dimensionless
Thermodynamic K uses activities; dimensionless.

📄Past Paper MCQs

📅 Actual MDCAT / NUMS Questions

50 MCQs
1For the equilibrium N₂O₄(g) ⇌ 2NO₂(g), the degree of dissociation (α) at total pressure P is related to K_p by K_p = 4α²P/(1-α²). If the pressure is quadrupled at constant temperature, the new value of α will:
MDCAT 2018 High-Difficulty Variant
  • A. Increase by a factor of 2.
  • B. Decrease, but K_p remains constant.
  • C. Remain unchanged.
  • D. Become exactly zero.
Answer: B
Pressure increase shifts equilibrium left, α decreases.
2In a system A(g) + B(g) ⇌ 2C(g) + D(g), the initial moles of A and B are in a 1:1 ratio. If 40% of A reacts at equilibrium, the total number of moles in the system (initially n) becomes:
NUMS 2021 Advanced Logic
  • A. 1.2n
  • B. 1.4n
  • C. 0.8n
  • D. 1.1n
Answer: A. 1.2n
For each A that reacts, total moles increase by 1; 40% reaction of 0.5n each → increase by 0.2n → total 1.2n.
3The equilibrium constant K_c for the reaction SO₂(g) + ½O₂(g) ⇌ SO₃(g) is K₁. What is the K_c for 2SO₃(g) ⇌ 2SO₂(g) + O₂(g)?
MDCAT 2015, 2023 Repeated
  • A. 1/K₁
  • B. 1/(K₁)²
  • C. √K₁
  • D. (K₁)²
Answer: B. 1/(K₁)²
Reverse and double coefficients → 1/(K₁)².
4At 500 K, the K_p for a reaction is 1 × 10⁻¹⁰ atm. If the reaction is exothermic (ΔH = -150 kJ/mol), at 1000 K, the value of K_p will be:
NUMS 2024 Thermal Dynamics
  • A. Significantly greater than 1 × 10⁻¹⁰.
  • B. Significantly smaller than 1 × 10⁻¹⁰.
  • C. Exactly 1 × 10⁻¹⁰.
  • D. 1 × 10¹⁰.
Answer: B
Exothermic: T↑ → K↓, so K_p becomes even smaller.
5For which reaction does the numerical value of K_p equal K_c(RT)⁻¹?
MDCAT 2017, 2022 Conceptual
  • A. H₂ + I₂ ⇌ 2HI
  • B. N₂ + 3H₂ ⇌ 2NH₃
  • C. PCl₅ ⇌ PCl₃ + Cl₂
  • D. 2NO + O₂ ⇌ 2NO₂
Answer: D
Δn = -1 → K_p = K_c(RT)⁻¹.
6In the reaction 3A + B ⇌ 2C, the units of K_c are:
MDCAT 2014, 2021
  • A. mol²·dm⁻⁶
  • B. dm⁶·mol⁻²
  • C. mol⁻²·dm⁶
  • D. dm³·mol⁻¹
Answer: C. mol⁻²·dm⁶
K_c = [C]²/[A]³[B]; units = (mol·dm⁻³)²/(mol·dm⁻³)⁴ = mol⁻²·dm⁶.
7A catalyst increases the rate of the forward reaction by 10⁶ times. The equilibrium constant (K_c) for the reaction in the presence of the catalyst will:
NUMS 2019, 2023
  • A. Increase by 10⁶.
  • B. Decrease by 10⁶.
  • C. Remain unchanged.
  • D. Change depending on the activation energy.
Answer: C
Catalyst does not change K_c.
8For the system C(s) + CO₂(g) ⇌ 2CO(g), if the partial pressure of CO₂ is doubled at equilibrium, the partial pressure of CO must increase by a factor of ______ to maintain equilibrium.
MDCAT 2019 Quantitative
  • A. 2
  • B. 4
  • C. √2
  • D. 1/2
Answer: C. √2
K_p = (P_CO)²/P_CO₂; if P_CO₂ doubles, P_CO must increase by √2.
9The reaction quotient Q_c for a system is 1.5 × 10³ while K_c is 1.5 × 10². The system will move:
NUMS 2020, 2022
  • A. Toward the products.
  • B. Toward the reactants.
  • C. Not at all (it is at equilibrium).
  • D. Toward the side with more moles of gas.
Answer: B
Q_c > K_c → reverse reaction.
10If ΔG° for a reaction is +50 kJ/mol, the equilibrium constant K is:
MDCAT 2024 Thermodynamic Link
  • A. K > 1
  • B. K < 1
  • C. K = 1
  • D. K = 0
Answer: B
ΔG° positive → K < 1.
11Adding Helium gas to the equilibrium N₂ + 3H₂ ⇌ 2NH₃ at constant pressure will:
NUMS 2021, 2024 Distinguisher
  • A. Shift the equilibrium to the right.
  • B. Shift the equilibrium to the left.
  • C. Have no effect.
  • D. Increase the K_p.
Answer: B
Adding inert gas at constant P increases volume, shifts to more moles (left).
12For an endothermic reaction, which plot represents the relationship between ln K_c and 1/T?
MDCAT 2022 Graphical
  • A. Straight line with a positive slope.
  • B. Straight line with a negative slope.
  • C. Horizontal line.
  • D. Exponential curve starting from origin.
Answer: B
Endothermic ΔH > 0; slope = -ΔH/R < 0.
13In the reaction 2A(g) ⇌ B(g) + Q kJ, a simultaneous increase in temperature and volume will:
NUMS 2022 Advanced Shift
  • A. Always shift equilibrium to the right.
  • B. Always shift equilibrium to the left.
  • C. Have opposing effects on the equilibrium position.
  • D. Increase the value of K_c.
Answer: C
Both factors can oppose each other's effect depending on direction of ΔH and Δn.
14Which of the following remains constant when the volume of the container is halved for the reaction PCl₅ ⇌ PCl₃ + Cl₂?
MDCAT 2016, 2023
  • A. Molar concentration of PCl₅.
  • B. Partial pressure of Cl₂.
  • C. Equilibrium constant K_c.
  • D. Total pressure.
Answer: C
K_c is constant at constant T.
15For the reaction 2SO₂ + O₂ ⇌ 2SO₃, the value of K_p / K_c is equal to:
NUMS 2018, 2023
  • A. RT
  • B. (RT)⁻¹
  • C. (RT)²
  • D. 1
Answer: B. (RT)⁻¹
Δn = -1 → K_p/K_c = (RT)⁻¹.
16At 1000°C, the equilibrium C(s) + H₂O(g) ⇌ CO(g) + H₂(g) is established. If the pressure is increased by reducing the volume, the amount of H₂ will:
MDCAT 2013, 2021
  • A. Increase.
  • B. Decrease.
  • C. Remain constant.
  • D. First increase then decrease.
Answer: B
More moles on product side, decrease V shifts left → H₂ decreases.
17Which condition favors the formation of NO(g) in the reaction N₂ + O₂ ⇌ 2NO (ΔH = +180 kJ/mol)?
NUMS 2020, 2024
  • A. Low temperature, High pressure.
  • B. High temperature, Low pressure.
  • C. High temperature, Independent of pressure.
  • D. Low temperature, Independent of pressure.
Answer: C
Endothermic → high T; Δn=0 → pressure no effect.
18In an exothermic equilibrium, the rate of the reverse reaction increases ______ than the rate of the forward reaction when the temperature is raised.
MDCAT 2017, 2022
  • A. Less
  • B. More
  • C. At the same rate
  • D. Negligibly
Answer: B
Increasing T raises reverse rate more (higher Ea for endothermic direction).
19For the system Ice ⇌ Water, the equilibrium is shifted toward the right by:
NUMS 2019, 2021
  • A. Increasing temperature.
  • B. Increasing pressure.
  • C. Decreasing pressure.
  • D. Adding an inhibitor.
Answer: B
Increase pressure favors liquid water (lower volume).
20The shift in equilibrium PCl₅ ⇌ PCl₃ + Cl₂ on addition of Cl₂ at constant volume is toward:
MDCAT 2015, 2023
  • A. The left, with an increase in PCl₅ concentration.
  • B. The right, with an increase in PCl₃ concentration.
  • C. The left, with K_c increasing.
  • D. No shift.
Answer: A
Adding product shifts equilibrium to left.
21The K_sp of Al(OH)₃ is 'x'. Its solubility 's' is given by:
MDCAT 2018, 2024 Mathematical
  • A. (x/4)^{1/3}
  • B. (x/27)^{1/4}
  • C. √x
  • D. (x/27)^{1/3}
Answer: B. (x/27)^{1/4}
K_sp = 27s⁴ → s = (x/27)^{1/4}.
22The solubility of AgCl (K_sp = 1 × 10⁻¹⁰) in 0.01 M AgNO₃ is:
NUMS 2021, 2023 Numerical
  • A. 1 × 10⁻⁵ M
  • B. 1 × 10⁻⁸ M
  • C. 1 × 10⁻¹² M
  • D. 1 × 10⁻¹⁰ M
Answer: B. 1 × 10⁻⁸ M
s = 10⁻¹⁰/0.01 = 10⁻⁸.
23Which of the following will have the highest solubility in water (K_sp for all is 1 × 10⁻¹²)?
MDCAT 2022 Conceptual
  • A. AB type salt.
  • B. A₂B type salt.
  • C. A₃B type salt.
  • D. A₃B₂ type salt.
Answer: D
Higher formula complexity gives larger s for same K_sp in high-order salts.
24When NaCl is added to a saturated solution of AgCl, the concentration of Ag⁺ ions:
NUMS 2018, 2022
  • A. Increases.
  • B. Decreases.
  • C. Remains the same.
  • D. Becomes equal to [Cl⁻].
Answer: B
Common ion Cl⁻ reduces [Ag⁺].
25If the Ionic Product (Q_sp) is exactly equal to K_sp, the solution is:
MDCAT 2016, 2021
  • A. Supersaturated.
  • B. Unsaturated.
  • C. Saturated.
  • D. Precipitating.
Answer: C. Saturated
Q_sp = K_sp → saturated.
26The K_sp of CaF₂ is 4 × 10⁻¹¹. The concentration of Ca²⁺ ions in its saturated solution is:
NUMS 2020, 2024
  • A. 2 × 10⁻⁴ M
  • B. 1 × 10⁻⁴ M
  • C. 3.1 × 10⁻⁴ M
  • D. 4 × 10⁻⁴ M
Answer: A. 2 × 10⁻⁴ M
s = (K_sp/4)^{1/3} = (10⁻¹¹)^{1/3} ≈ 2.15×10⁻⁴; [Ca²⁺] = s ≈ 2.15×10⁻⁴ → 2×10⁻⁴.
27The common ion effect is used in Group II of qualitative analysis to ______ the concentration of S²⁻ ions.
MDCAT 2014, 2023
  • A. Increase
  • B. Decrease
  • C. Keep constant
  • D. Neutralize
Answer: B
HCl provides H⁺, reducing S²⁻ concentration.
28Which pair of compounds will exhibit the "Common Ion Effect"?
NUMS 2019, 2022
  • A. NaCl and KNO₃
  • B. HCl and CH₃COOH
  • C. NH₄Cl and KOH
  • D. AgCl and BaCl₂
Answer: D
AgCl and BaCl₂ share Cl⁻.
29The solubility of PbI₂ is 0.0013 mol/dm³. Its K_sp value is:
MDCAT 2015, 2021
  • A. 1.7 × 10⁻⁶
  • B. 8.7 × 10⁻⁹
  • C. 4.4 × 10⁻¹⁰
  • D. 2.2 × 10⁻⁹
Answer: B. 8.7 × 10⁻⁹
K_sp = 4s³ = 4×(0.0013)³ ≈ 8.8×10⁻⁹.
30A precipitate of AgCl dissolves in NH₄OH due to the formation of:
NUMS 2021, 2023
  • A. [Ag(NH₃)₂]Cl
  • B. AgOH
  • C. NH₄Cl
  • D. [Ag(NH₃)₄]Cl₂
Answer: A
Forms soluble diamminesilver(I) chloride.
31A buffer solution with pH = 9 can be prepared by mixing:
MDCAT 2017, 2022
  • A. CH₃COOH and CH₃COONa (pK_a = 4.74)
  • B. NH₄OH and NH₄Cl (pK_b = 4.74)
  • C. H₃PO₄ and NaH₂PO₄
  • D. NaOH and NaCl
Answer: B
pOH = 14-9=5; pK_b=4.74, buffer near pK_b.
32If the ratio of [Salt]/[Acid] in an acidic buffer is increased 10 times, the pH will:
NUMS 2020, 2024 Advanced
  • A. Increase by 1.
  • B. Decrease by 1.
  • C. Increase by 10.
  • D. Remain the same.
Answer: A. Increase by 1
log(10) = 1, pH increases by 1.
33The pOH of a buffer containing 0.1 M NH₄OH and 0.01 M NH₄Cl (pK_b = 4.74) is:
MDCAT 2018, 2023 Numerical
  • A. 4.74
  • B. 5.74
  • C. 3.74
  • D. 9.26
Answer: C. 3.74
pOH = pK_b + log(0.01/0.1) = 4.74 - 1 = 3.74.
34Buffer capacity is maximum when:
NUMS 2019, 2022
  • A. pH = 7
  • B. pH = pK_a
  • C. [Salt] = 10 × [Acid]
  • D. pH = 1
Answer: B. pH = pK_a
Maximum capacity at pH = pK_a.
35The pH of a solution containing 0.1 M CH₃COONa and 0.1 M CH₃COOH (K_a = 1.8 × 10⁻⁵) is:
MDCAT 2014, 2021
  • A. 4.74
  • B. 9.26
  • C. 7.0
  • D. 5.0
Answer: A. 4.74
pH = pK_a = -log(1.8e-5) ≈ 4.74.
36Which of the following is an "Alkaline Buffer"?
NUMS 2021, 2024
  • A. HCN + NaCN
  • B. NH₃ + NH₄Cl
  • C. HCOOH + HCOONa
  • D. HCl + NaCl
Answer: B. NH₃ + NH₄Cl
Weak base + its salt.
37The Henderson-Hasselbalch equation for a basic buffer is:
MDCAT 2016, 2022
  • A. pH = pK_b + log [Salt]/[Base]
  • B. pOH = pK_b + log [Salt]/[Base]
  • C. pOH = pK_b - log [Salt]/[Base]
  • D. pH = 14 + pOH
Answer: B
For basic buffer: pOH = pK_b + log([salt]/[base]).
38The pH of human blood is maintained by the HCO₃⁻ / H₂CO₃ system. If the CO₂ level in the blood increases (acidosis), the equilibrium shifts to produce more:
NUMS 2022 Physiological
  • A. OH⁻
  • B. H⁺
  • C. CO₃²⁻
  • D. O₂
Answer: B. H⁺
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻; increase CO₂ shifts right, producing H⁺.
39Adding 0.01 moles of NaOH to 1 liter of a buffer containing 0.1 M HA and 0.1 M A⁻ results in a [Salt]/[Acid] ratio of:
MDCAT 2023 Calculation
  • A. 1:1
  • B. 0.11 : 0.09
  • C. 0.09 : 0.11
  • D. 1.1 : 0.9
Answer: B
NaOH converts HA to A⁻: HA decreases to 0.09, A⁻ increases to 0.11.
40A mixture of NH₄Cl and NH₄OH resists pH change when HCl is added because H⁺ reacts with:
NUMS 2018, 2021
  • A. NH₄⁺
  • B. OH⁻ from NH₄OH
  • C. Cl⁻
  • D. H₂O
Answer: B
OH⁻ neutralizes added H⁺.
41In Haber’s process, the yield of NH₃ is 30% at equilibrium. If we use a more efficient catalyst, the yield will:
MDCAT 2019, 2024 Topper-Tier
  • A. Increase to 50%.
  • B. Decrease to 10%.
  • C. Remain at 30%.
  • D. Become 100%.
Answer: C
Catalyst does not change equilibrium yield.
42The heat of reaction for N₂ + 3H₂ ⇌ 2NH₃ is -92 kJ. This indicates that:
NUMS 2020, 2023
  • A. High temperature favors NH₃.
  • B. Low temperature favors NH₃.
  • C. Temperature has no effect on yield.
  • D. The reaction is endothermic.
Answer: B
Exothermic → low T favors products.
43The pressure used in Haber's process (200 atm) is a "Compromise Pressure" because:
MDCAT 2017, 2022
  • A. Lower pressure gives more yield.
  • B. Higher pressure is too expensive and dangerous to maintain.
  • C. Pressure does not affect this reaction.
  • D. It prevents the catalyst from melting.
Answer: B
Higher pressure is costly/risky.
44Which gas is removed from the Haber's reactor to shift equilibrium forward?
NUMS 2021
  • A. N₂
  • B. H₂
  • C. NH₃ (by liquefaction)
  • D. CH₄
Answer: C. NH₃
Remove NH₃ to shift equilibrium right.
45The iron catalyst in Haber's process is "Promoted" by:
MDCAT 2014, 2021
  • A. MgO
  • B. Al₂O₃ and K₂O
  • C. Pt
  • D. V₂O₅
Answer: B. Al₂O₃ and K₂O
Promoters: Al₂O₃ and K₂O.
46What is the K_p expression for Haber's process?
NUMS 2019, 2024
  • A. P²_NH₃ / (P_N₂ · P³_H₂)
  • B. (P_N₂ · P³_H₂) / P²_NH₃
  • C. P_NH₃ / (P_N₂ · P_H₂)
  • D. P²_NH₃ · P_N₂ · P³_H₂
Answer: A
K_p = (P_NH₃)² / (P_N₂)(P_H₂)³.
47Decreasing the volume of the Haber's reaction vessel by 2 times increases the rate of forward reaction by ______ times.
MDCAT 2023 Kinetic Link
  • A. 2
  • B. 4
  • C. 8
  • D. 16
Answer: D. 16
Rate ∝ [N₂][H₂]³; halving volume doubles concentration; rate change = 2×2³ = 16.
48In Haber’s process, the N₂ gas is obtained from:
NUMS 2018, 2022
  • A. Natural gas.
  • B. Fractional distillation of liquid air.
  • C. Electrolysis of water.
  • D. Decomposition of NH₄NO₃.
Answer: B
N₂ from liquid air.
49The reaction N₂ + 3H₂ ⇌ 2NH₃ shows Δn equal to:
MDCAT 2015, 2021
  • A. +2
  • B. -2
  • C. 0
  • D. -4
Answer: B. -2
Δn = 2 - (1+3) = -2.
50At equilibrium, if [N₂] = 2 M, [H₂] = 3 M, and [NH₃] = 4 M, the value of K_c is:
NUMS 2022 Calculation
  • A. 4/54
  • B. 16/54
  • C. 8/27
  • D. 16/18
Answer: B. 16/54
K_c = (4)²/(2·3³) = 16/54.

🔍Direct Search Queries — Chemical Equilibrium

Exact search terms students use on Google for this chapter. Click any to jump to the relevant section:

chemical equilibrium MDCAT notes reversible reactions and dynamic equilibrium Kc and Kp relationship Le Chatelier's principle effect of concentration on equilibrium effect of pressure on equilibrium effect of temperature on equilibrium effect of catalyst on equilibrium solubility product Ksp ionic product vs solubility product common ion effect examples buffer solution types acidic vs basic buffer Henderson-Hasselbalch equation buffer capacity definition blood buffer system pH Haber process conditions ammonia synthesis conditions Haber process Le Chatelier promoters K2O Al2O3 what is chemical equilibrium why is equilibrium dynamic difference between Kc and Kp what is Le Chatelier principle what is Ksp in chemistry what is common ion effect what is a buffer solution how does Haber process work chemical equilibrium MCQs with answers chemical equilibrium MCQs pdf Le Chatelier MCQs MDCAT past papers chemical equilibrium NUMS chemistry past papers UHS chemistry MCQs chemical equilibrium chapter notes class 11 buffer solutions class 11 chemistry Ksp calculations class 11 notes Haber process class 11 notes

❔Frequently Asked Questions

What is chemical equilibrium?
Chemical equilibrium is the state in a reversible reaction when the rate of the forward reaction equals the rate of the reverse reaction. Concentrations of reactants and products remain constant (dynamic equilibrium), although the reaction has not stopped.
What are macroscopic characteristics of equilibrium?
The reaction occurs in a closed system, concentrations of reactants and products remain constant over time, and measurable properties like colour, density, and pressure remain unchanged — although molecular processes continue at the microscopic level.
What is Le Chatelier's principle?
Le Chatelier's principle states that if a system at equilibrium is subjected to a change (stress), the system shifts in the direction that counteracts the imposed change. This applies to changes in concentration, pressure, temperature, or catalyst addition.
What is the equilibrium constant Kc?
Kc is the ratio of the product of product concentrations to the product of reactant concentrations, each raised to the power of their stoichiometric coefficients. It depends only on temperature and is independent of initial concentrations.
What is the difference between Kc and Kp?
Kc uses molar concentrations; Kp uses partial pressures. They are related by Kp = Kc(RT)^Δn, where Δn is the change in moles of gas.
What is the significance of a large vs small Kc?
A large Kc (>1) means products are strongly favoured (reaction nearly complete). A small Kc (<1) means reactants are favoured (reaction barely proceeds forward). Kc = 1 means both are comparable at equilibrium.
What is the solubility product Ksp?
Ksp is the equilibrium constant for the dissolution of a sparingly soluble salt. For salt AmBn, Ksp = [A]^m[B]^n. It depends only on temperature.
What is the common ion effect?
The common ion effect is the decrease in solubility of a salt when a second compound containing one of the same ions is present. It is explained by Le Chatelier's principle — the common ion shifts the dissolution equilibrium to the left.
What is a buffer solution?
A buffer is a solution that resists change in pH when small amounts of acid or base are added. Acidic buffers (e.g., CH3COOH/CH3COONa) have pH<7; basic buffers (e.g., NH3/NH4Cl) have pH>7.
What is the Henderson-Hasselbalch equation?
For acidic buffer: pH = pKa + log([A⁻]/[HA]). For basic buffer: pOH = pKb + log([salt]/[base]). It gives the pH of a buffer based on the ratio of salt to acid/base.
When is buffer capacity maximum?
Buffer capacity is maximum when [Salt] = [Acid] (for acidic buffer) or [Salt] = [Base] (for basic buffer), i.e., when pH = pKa (or pOH = pKb).
What is the Haber process?
The Haber process is the industrial synthesis of ammonia from nitrogen and hydrogen: N2 + 3H2 ⇌ 2NH3 (ΔH = -92 kJ). It uses high pressure (200-300 atm), moderate temperature (400-450°C), and an iron catalyst with K2O/Al2O3 promoters.
Why is high pressure used in Haber process?
High pressure favours the side with fewer moles of gas. In N2 + 3H2 ⇌ 2NH3, 4 moles of gas produce 2 moles, so high pressure shifts equilibrium right, increasing ammonia yield.
Why is 450°C used in Haber process despite it being exothermic?
450°C is a compromise temperature. Lower T favours NH3 thermodynamically but slows the rate; higher T increases rate but reduces yield. 450°C balances both, giving acceptable yield at reasonable rate.
What does a catalyst do in Haber process?
The iron catalyst increases the rate at which equilibrium is reached. It does not shift the equilibrium position or change the equilibrium constant.
How does temperature affect Kc?
For exothermic reactions, increasing T decreases Kc. For endothermic reactions, increasing T increases Kc. Kc changes only with temperature — not with concentration, pressure, or catalyst.
What is reaction quotient Q?
Q is the same expression as Kc but calculated with current (non-equilibrium) concentrations. If Q < Kc, reaction proceeds forward; if Q > Kc, reaction goes reverse; if Q = Kc, system is at equilibrium.
Does adding an inert gas shift equilibrium?
Adding inert gas at constant volume: no shift (partial pressures unchanged). At constant pressure: volume increases, shifting equilibrium toward the side with more moles of gas.
How many MCQs come from Chemical Equilibrium in MDCAT?
Chemical Equilibrium typically contributes 3–5 MCQs out of 81 Chemistry MCQs in MDCAT.
Which topics from Chemical Equilibrium are most frequently asked in MDCAT?
Le Chatelier's principle applications, Kc vs Kp relationship, effect of temperature/pressure on equilibrium, Ksp calculations, common ion effect, buffer pH calculations, Henderson-Hasselbalch equation, and Haber process conditions.

📚Other Chemistry Chapters

1
Fundamental Principles of Organic Chemistry
2
Hydrocarbons
3
Alkyl Halides
4
Alcohols and Phenols
5
Aldehydes and Ketones
6
Carboxylic Acids
7
Macromolecules
8
Chemistry of Life

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