Characterstics and Factors Influencing Equilibrium constant

Characteristics of Equilibrium Constant

1. It has a definite value for every chemical reaction at a given temperature.

2. It is independent of concentrations of the reactants and products.

3. It is not effected by the presence of catalyst.

4. It is a convenient measure of the extent to which the reaction proceeds in a particular direction at a given temperature.


Factors Influencing Equilibrium Constant

1. Stoichiometic representation of reaction: Consider the following reactions:

N_2 + O_2 \rightleftharpoons 2NO \hspace{3mm} \text{and} \hspace{3mm} \dfrac{1}{2}N_2 + \dfrac{1}{2}O_2 \leftrightharpoons NO


K_c = \dfrac{[NO]^2}{[N_2][O_2]} K_c = \dfrac{[NO]}{[N_2]^{1/2}[O_2]^{1/2} } \\[3mm] \therefore K_c = (K_c)^2


2. The mode of representing the change: Consider the equilibrium mixture of N_2, O_2 \text{and} NO

N_2 + O_2 \leftrightharpoons 2NO \hspace{3mm} \text{and} \hspace{3mm} 2NO \rightleftharpoons N_2 + O_2





\therefore K_c = 1/K_c


3. Temperature: Equilibrium constant changes with temperature as:

\log_{10} \dfrac{K_2}{K_1} = \dfrac{\Delta H}{2.303}[\dfrac{T_2- T_1}{T_1T_2}]


Where \Delta H is change in enthalpy of the reaction, other terms are as usual.


Importance of equilibrium constant:

(i)                  To find equilibrium concentrations


(ii)                 To find the measurement of extent of reaction.

Extent of forward reaction \propto K

I.e. Higher value of K_c or K_p means reaction is going to complete.


(iii) Stability of products \propto K_c or K_p

N_2 + O_2 \leftrightharpoons 2NO_2, K_c = 8.7 \times 10^{-10}


N_2 + O_2 \leftrightharpoons 2NO, K_c = 6.5 \times 10^{-16}

i. e., NO_2 is more stable then NO here.

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