The thermal dissociation equilibrium of $\mathrm{CaCO}_{3}(s)$ is studied under different conditions. $\mathrm{CaCO}_{3}(\mathrm{~s}) \rightleftharpoons \mathrm{CaO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{~g})$ For this equilibrium, the correct statement(s) is(are)

(A) $\Delta H$ is dependent on $T$; (B) $K$ is independent of the initial amount of $\mathrm{CaCO}_{3}$; (D) $\Delta H$ is independent of the catalyst, if any

(C) $K$ is dependent on the pressure of $\mathrm{CO}_{2}$ at a given $T$

JEE Advanced · 2013 · 02 Jun 2013 · Paper 2 · Equilibrium

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The thermal dissociation equilibrium of

CaCO_{3} (s)

is studied under different conditions.

CaCO_{3} (s) ⇌ CaO (s) + CO_{2} (g)

For this equilibrium, the correct statement(s) is(are)

(A) $Δ H$ is dependent on $T$ ✓ Correct
(B) $K$ is independent of the initial amount of $CaCO_{3}$ ✓ Correct
(C) $K$ is dependent on the pressure of $CO_{2}$ at a given $T$
(D) $Δ H$ is independent of the catalyst, if any✓ Correct

Answer: (A), (B), (D)

Solution

For the equilibrium

CaCO_{3} (s) ⇌ CaO (s) + CO_{2} (g)

:

(A)

Δ H

varies slightly with temperature due to heat capacity effects (van't Hoff equation:

ln K = - \frac{Δ H}{R T} + C

).

(B) The equilibrium constant

K

depends only on temperature, not on the initial amounts of reactants or products.

(C) At a given temperature,

K

is a constant and does not depend on the pressure of

CO_{2}

. The pressure affects the position of equilibrium but not

K

itself.

(D)

Δ H

is a thermodynamic property independent of the reaction pathway or presence of a catalyst. A catalyst only affects the rate, not the thermodynamics.

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JEE Advanced · 2013 · 02 Jun 2013 · Paper 2 · Equilibrium

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