CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
Nitrogen tetroxide, N₂O₄(g), dissociates into nitrogen dioxide, NO₂(g), according to the equation
N₂O₄(g) ⇌ 2 NO₂(g).
At 298 K the standard Gibbs free energy change for the forward reaction is ΔG° = +4.8 kJ mol⁻¹. A sealed 1.00 L rigid vessel at 298 K initially contains 0.010 mol of N₂O₄(g) and 0.090 mol of NO₂(g). (Assume ideal-gas behavior throughout.)
(1) Calculate the numerical value of the reaction quotient, Q, for the forward reaction using the initial amounts in the vessel.
(2) Explain, without performing any further numerical calculation, whether Q is greater than, less than, or equal to the equilibrium constant, K, for the reaction at 298 K. Justify your answer in terms of the sign of ΔG for the forward reaction at the stated conditions.
(3) Describe qualitatively how the composition of the gas mixture (relative amounts of N₂O₄ and NO₂) will change spontaneously, if at all, as the system moves toward equilibrium at 298 K.