The following gas-phase reactions occur separately at the same temperature
CHEMISTRY · Subjective · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
The following gas-phase reactions occur separately at the same temperature, and each reaches equilibrium within a sealed container of identical volume.
Reaction 1: A(g)+B(g)⇌C(g) with Kc=3.5×108
Reaction 2: D(g)⇌2E(g) with Kc=2.1×10−9
Reaction 3: F(g)+G(g)⇌H(g) with Kc=0.80
A student prepares equimolar initial amounts (0.100 mol of each reactant species) in separate containers for the three reactions.
(a) Rank the three reactions from greatest to least extent of conversion of reactants to products at equilibrium. Justify your ranking in terms of the magnitude of each equilibrium constant.
(b) For Reaction 2, estimate (no calculation required) whether more than 1 % of the initial amount of D will have been converted to E at equilibrium. Explain your reasoning.
(c) Another student asserts, “Because the Kc value of Reaction 3 is less than 1, essentially no product H will be present at equilibrium.” Evaluate this assertion and provide a quantitative or qualitative argument that supports your evaluation.
(d) Comment on whether any information in the Kc values allows one to predict how quickly each reaction will reach equilibrium. Provide a brief justification.