CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
Inside a muscle cell, the reversible reaction below helps regulate the cellular redox environment: GSSG(aq)+NADPH(aq)⇌2GSH(aq)+NADP+(aq). At physiological temperature, the equilibrium constant for this reaction is Kc=1.1×104. Under resting conditions, the intracellular concentrations are approximately: [GSSG]=2.0×10−4molL−1, [NADPH]=5.0×10−3molL−1, [GSH]=8.0×10−3molL−1, and [NADP+]=1.0×10−3molL−1. During intense exercise, rapid metabolic activity transiently alters the concentrations to: [GSSG]=4.0×10−4molL−1, [NADPH]=2.0×10−3molL−1, [GSH]=6.0×10−3molL−1, and [NADP+]=5.0×10−3molL−1.
(a) Compute the reaction quotient Qc for the system under exercise conditions.
(b) Compare Qc with Kc and predict the spontaneous direction in which the net reaction will proceed as the cell returns to homeostasis. Provide chemical reasoning for your prediction.
(c) State the sign of ΔG for the forward reaction immediately after the metabolic shift, and relate this sign to your conclusion in part (b).
(d) Explain how the predicted reaction direction helps restore the cellular redox balance during recovery from exercise.