CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
Dinitrogen tetroxide, N2O4(g), decomposes according to the balanced equation
N2O4(g) ⇌ 2 NO2(g)
At 400 K the equilibrium constant for this reaction in terms of concentration is Kc = 5.0 × 10⁻³. A sealed 2.0 L flask at 400 K contains a gaseous mixture in which [N2O4] = 0.020 M and [NO2] = 0.060 M. The reaction quotient for the mixture has already been calculated to be Qc = 1.8 × 10⁻².
Answer the following questions about this system.
(a) Describe the chemical significance of the reaction quotient Qc for this system and explain how it differs conceptually from the equilibrium constant Kc.
(b) Compare the given values of Qc and Kc and predict the direction in which the reaction will proceed to achieve equilibrium. Justify your prediction in terms of relative reactant and product concentrations.
(c) Identify which species’ concentration is expected to increase as the system approaches equilibrium and explain the reasoning behind your choice.