Chapter 13

Q. 13.1

Writing Equilibrium Equations for Gas-Phase Reactions

Write the equilibrium equation for each of the following reactions:

(a) N_2(g) + 3 H_2(g) \rightleftharpoons 2 NH_3(g)

(b) 2 NH_3(g) \rightleftharpoons N_2(g) + 3 H_2(g)


Put the concentrations of the reaction products in the numerator of the equilibrium-constant expression and the concentrations of the reactants in the denominator. Then raise the concentration of each substance to the power of its coefficient in the balanced chemical equation.


Verified Solution

\text { (a) } K_{\mathrm{c}}=\frac{\left[\mathrm{NH}_3\right]^{2 \  \leftarrow \ Coefficient \ of \ NH_3}}{\left[\mathrm{~N}_2\right]\left[\mathrm{H}_2\right]^{3 \ \leftarrow \ Coefficient \ of \ H_2}}

(b) K_{\mathrm{c}}{ }^{\prime}=\frac{\left[\mathrm{N}_2\right]\left[\mathrm{H}_2\right]^{3 \ \leftarrow \ Coefficient \ of \ H_2}}{\left[\mathrm{NH}_3\right]^{2 \ \leftarrow \ Coefficient \ of \ NH_3}} \ \ \ \ \ \ \ \ K_c{ }^{\prime}=\frac{1}{K_c}

Because the balanced equation in part (b) is the reverse of that in part (a), the equilibrium-constant expression in part (b) is the reciprocal of the expression in part (a) and the equilibrium constant K_{c}^{ʹ} is the reciprocal of K_c