The equilibrium constant in terms of partial pressures for the reaction is at 350 K.

CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)

Problem

The equilibrium constant in terms of partial pressures for the reaction 2 NOCl(g)  ⇌  2 NO(g)+Cl2(g)2\,\text{NOCl}(g)\;\rightleftharpoons\;2\,\text{NO}(g)+\text{Cl}_2(g) is Kp=1.8×10−4K_{p}=1.8\times10^{-4} at 350 K. (a) Determine the value of the equilibrium constant Kp′K_{p}' at the same temperature for the equation NOCl(g)  ⇌  NO(g)+12 Cl2(g)\text{NOCl}(g)\;\rightleftharpoons\;\text{NO}(g)+\tfrac12\,\text{Cl}_2(g). (b) A reaction vessel at 350 K initially contains the following partial pressures: PNOCl=0.350 atmP_{\text{NOCl}}=0.350\,\text{atm}, PNO=0.050 atmP_{\text{NO}}=0.050\,\text{atm}, and PCl2=0.020 atmP_{\text{Cl}_2}=0.020\,\text{atm}. Calculate the reaction quotient Qp′Q_{p}' for the equation in part (a) and predict the direction in which the system will shift to reach equilibrium. (c) Provide a concise explanation of why altering stoichiometric coefficients changes the exponents that appear in the equilibrium‐constant expression, and discuss how this ensures that the numerical value of KpK_{p} (or Kp′K_{p}') remains dimensionless even though partial pressures carry units.

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