Reaction 1: Reaction 2: Both reactions occur sequentially in a biochemical pathway

CHEMISTRY · Single correct · A Level · Chemistry · Thermodynamics · Thermodynamics

Problem

Reaction 1: X→Y\text{X} \rightarrow \text{Y} ΔG∘=+15 kJ mol−1\Delta G^\circ = +15\,\text{kJ mol}^{-1} Reaction 2: Y→Z\text{Y} \rightarrow \text{Z} ΔG∘=−35 kJ mol−1\Delta G^\circ = -35\,\text{kJ mol}^{-1} Both reactions occur sequentially in a biochemical pathway. Which statement best explains why the overall conversion of X to Z is spontaneous under standard conditions? (a) An enzyme that catalyzes Reaction 1 lowers its activation energy, which converts its ΔG∘\Delta G^\circ from positive to negative and makes the overall pathway spontaneous. (b) The algebraic sum of the two ΔG∘\Delta G^\circ values is negative, making the net process thermodynamically favorable. (c) Reaction 2 releases enough heat to raise the temperature, so the added thermal energy drives Reaction 1 forward under standard conditions. (d) The intermediate Y will build up until its high concentration forces Reaction 1 to go to completion according to Le Châtelier’s principle.

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