The overall reaction has

CHEMISTRY · Single correct · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry

Problem

The overall reaction 6 CO2(g)+6 H2O(l)→C6H12O6(aq)+6 O2(g)6\,\text{CO}_2(g)+6\,\text{H}_2\text{O}(l)\rightarrow\text{C}_6\text{H}_{12}\text{O}_6(aq)+6\,\text{O}_2(g) has ΔG∘=+2.9×103 kJ mol−1\Delta G^\circ=+2.9\times10^3\,\text{kJ mol}^{-1}. Which of the following best explains how this reaction proceeds in green plants under standard conditions? (a) Continual removal of the O2(g)\text{O}_2(g) produced shifts the equilibrium toward products, effectively making ΔG∘\Delta G^\circ negative. (b) The presence of specific enzymes lowers the standard free energy change, making the reaction spontaneous without any additional energy input. (c) Absorption of visible light excites electrons in chlorophyll, providing the energy required to drive the non-spontaneous reduction of CO2\text{CO}_2. (d) Coupling the reaction to the hydrolysis of a single mole of ATP (ΔG∘≈−30 kJ mol−1\Delta G^\circ \approx -30\,\text{kJ mol}^{-1}) supplies enough energy to render the overall process thermodynamically favorable.

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