Question:

The thermal dissociation of equilibrium of $CaCO_3 $ (s) is studied under different conditions $ CaCO_3 \, ( g) \rightleftharpoons CaCO ( g ) + CO_2 ( g)$ For this equilibrium, the correct statement(s) is/are

Updated On: Jun 23, 2023
  • $\triangle$ H is dependent on T
  • K is independent of the initial amount of $CaCO_3$
  • K is dependent on the pressure of $CO_2$ at a given T
  • $\triangle$ H is independent of the catalyst, if any
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The Correct Option is D

Solution and Explanation

PLAN Heat of reaction is dependent on temperature (Kirchhoff's equation) in heterogeneous system, equilibrium constant is independent on the molar concentration of solid species. Heat of reaction is not affected by catalyst. It lowers activation energy. $ CaCO_3 \, ( g) \rightleftharpoons CaCO ( g ) + CO_2 ( g)$ By KirchhofFs equation, $\triangle H_2^o \, (at \, T_2) = \triangle H_1^o \, (at \, T_1 ) + \triangle C_p ( T_2 - T_1 ) $ $\triangle H^\circ$ varies with temperature. Thus, (a) is correct. $ K = p_{ CO_2 } $ K is dependent on pressure of $CO_2$ but independent of molar concentration of $ CaCO_3$, Thus, (b) and (c) are correct. At a given temperature, addition of catalysis lowers activaion energy, $\triangle$H remaining constant. Thus, (d) is also correct. $E_a$ = Activation energy in absence of catalyst $E_a$' = Activation energy in presence of catalyst
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Concepts Used:

Equilibrium

An equilibrium represents a state in a process when the observable properties such as color, temperature, pressure, concentration etc do not show any change.

The word equilibrium means ‘balance’ which indicates that a chemical reaction represents a balance between the reactants and products taking part in the reaction. The equilibrium state is also noticed in certain physical processes such as the melting point of ice at 0℃, both ice and water are present at equilibrium.

In the case of physical processes such as the melting of solid, dissolution of salt in water etc., the equilibrium is called physical equilibrium while the equilibrium associated with chemical reaction is known as chemical equilibrium.

Equilibrium in Chemical changes

The chemical equilibrium in a reversible reaction is the state at which both forward and backward reactions occur at the same speed.

The stage of the reversible reaction at which the concentration of the reactants and products do not change with time is called the equilibrium state.

Read More: Calculating Equilibrium Concentration

Types of Chemical Equilibrium

There are two types of chemical equilibrium:

  • Homogeneous Equilibrium
  • Heterogeneous Equilibrium

Homogenous Chemical Equilibrium

In this type, the reactants and the products of chemical equilibrium are all in the same phase. Homogenous equilibrium can be further divided into two types: Reactions in which the number of molecules of the products is equal to the number of molecules of the reactants. For example,

  • H2 (g) + I2 (g) ⇌ 2HI (g)
  • N2 (g) + O2 (g) ⇌ 2NO (g)

Reactions in which the number of molecules of the products is not equal to the total number of reactant molecules. For example,

  • 2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
  • COCl2 (g) ⇌ CO (g) + Cl2 (g)

Heterogeneous Chemical Equilibrium

In this type, the reactants and the products of chemical equilibrium are present in different phases. A few examples of heterogeneous equilibrium are listed below.

  • CO2 (g) + C (s) ⇌ 2CO (g) 
  • CaCO3 (s) ⇌ CaO (s) + CO2 (g)

Thus, the different types of chemical equilibrium are based on the phase of the reactants and products.

Check Out: Equilibrium Important Questions