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Equilibrium Constant - Practice Questions & MCQ

Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET

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  • Types of Equilibrium Constant is considered one of the most asked concept.

  • 9 Questions around this concept.

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The equilibrium constant (KC) for the reaction \mathrm{N_{2}\left ( g \right )+O_{2}(g)\rightarrow 2NO(g)} at temperature T is  4\times 10^{-4}. The value of KC for the given reaction at the same temperature is : 

\mathrm{NO(g)\rightarrow \frac{1}{2} \: N_{2}(g)+\frac{1}{2}\: O_{2}(g)}

A vessel at 1000 K contains CO2 with a pressure of 0.5 atm. Some of the CO2 is converted into CO on the addition of graphite. If the total pressure at equilibrium is 0.8 atm, the value of K is

Concepts Covered - 1

Types of Equilibrium Constant

It is the ratio of rate of forward and backward reaction at a particular temperature or it is the ratio of active masses of the reactants to that of active masses of products at a particular temperature raised to their stoichiometric cofficients. It is denoted by Kc or Kp. The distinction between Keq and Kis that expression of Keq involves all the species (whether they are pure solids, pure liquids, gases, solvents or solutions) while the expression Kinvolves only those species whose concentration is a variable (gases and solution). It means Kis a devoid of pure components (like pure solids and pure liquids) and solvents.

Let us look at the definition of Equilibrium constant in terms of concentration and partial pressure

(1) Equilibrium constant in terms of Concentration

For a reaction:

\mathrm{mA+nB \rightleftharpoons pC+qD}

\mathrm{r _{forward} \propto[ A ]^m[ B ]^n= K _{f}[ A ]^m[ B ]^n}

\mathrm{r _{backward} \propto[ C ]^p[ D ]^q= K _{b}[ C ]^p[ D ]^q}

We know that at equilibrium

\mathrm{r_f = r_b}

\mathrm{K _{f}[ A ]^m[ B ]^n= K _{b}[ C ]^p[ D ]^q}

\mathrm{\frac{K_{f}}{K_{b}}\: =\: \frac{[C]^p[D]^q}{[A]^m[B]^n}\: \: \: \: (at \: constant\: temperature)}

\mathrm{\frac{K_{f}}{K_{b}}\: =\: \frac{[C]^p[D]^q}{[A]^m[B]^n}= K_c}

The above expression gives us the value of Kc as the activity or the active mass is expressed in terms of the concentrations (c) or the molarity


(2) Equilibrium constant in terms of Partial pressure

In this case, the equilibrium constant is known as Kp. It is applicable only for gaseous systems.
For the reaction:

\mathrm{mA+nB \rightleftharpoons pC+qD}

\mathrm{r _{forward} \propto P_A ^m\ P_B ^n= K _{f_1} P_A ^m\ P_B ^n}

\mathrm{r _{backward} \propto P_C ^p\ P_D ^q= K _{b_1} P_C ^p\ P_D ^q}

At equilibrium

\mathrm{r_f = r_b}

\mathrm{K _{f_1}P_A ^m\ P_ B^n= K _{b_1} P_C ^p\ P_D ^q}

\mathrm{K_P=\frac{K_{f_1}}{K_{b_2}}\: =\: \frac{P_C ^p\ P_D ^q}{P_A ^m\ P_B ^n}}

The above expression gives us the value of Kas the activity is expressed in terms of the partial pressures.

Note: This is generally used for gaseous systems or systems where gases are in equilibrium with liquids or solids

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Types of Equilibrium Constant

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Reference Books

Types of Equilibrium Constant

Chemistry Part I Textbook for Class XI

Page No. : 198

Line : 38

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