Question

Which of the following reactions lies to the right, favoring the formation of products, and which lies to the left, favoring formation of reactants? (a) $2\mathrm{NO}(g)+{\mathrm{O}}_2(g)\rightleftharpoons 2{\mathrm{NO}}_2(g);K_p=5.0\times {10}^{12}$ (b) $2\mathrm{HBr}(g)\rightleftharpoons {\mathrm{H}}_2(g)+{\mathrm{Br}}_2(g);K_c=5.8\times {10}^{-18}$

Short answer

Reaction (a) lies to the right, favoring the formation of products, since $K_p=5.0\times {10}^{12}$ which is greater than 1. Reaction (b) lies to the left, favoring the formation of reactants, since $K_c=5.8\times {10}^{-18}$ which is less than 1.

Step-by-step solution

Reaction (a) Direction

For reaction (a), we have: $2\mathrm{NO}(g)+{\mathrm{O}}_2(g)\rightleftharpoons 2{\mathrm{NO}}_2(g)$ The equilibrium constant Kp is given as: $K_p=5.0\times {10}^{12}$ Since the value of $K_p$ is greater than 1, this means that the reaction favors the formation of products. Therefore, reaction (a) lies to the $\boxed{{\displaystyle right}}$.

Reaction (b) Direction

For reaction (b), we have: $2\mathrm{HBr}(g)\rightleftharpoons {\mathrm{H}}_2(g)+{\mathrm{Br}}_2(g)$ The equilibrium constant Kc is given as: $K_c=5.8\times {10}^{-18}$ Since the value of $K_c$ is less than 1, this means that the reaction favors the formation of reactants. Therefore, reaction (b) lies to the $\boxed{{\displaystyle left}}$.