Which of the following reactions could be coupled to an...

Which of the following reactions could be coupled to an endergonic reaction with $\Delta G=+3.56 \mathrm{kJ} / \mathrm{mol}$ ? (a) $\mathrm{A} \rightarrow \mathrm{B}, \Delta G=+6.08 \mathrm{k} / \mathrm{mol}$ (b) $C \rightarrow D, \Delta G=+3.56 \mathrm{kJ} / \mathrm{mol}$ (c) $E \rightarrow F, \Delta G=0 \mathrm{k} / \mathrm{mol}$ (d) $G \rightarrow H, \Delta G=-1.22 \mathrm{kJ} / \mathrm{mol}$ (e) $1 \rightarrow 1, \Delta G=-5.91 \mathrm{kJ} / \mathrm{mol}$

Which of the following reactions could be coupled to an endergonic reaction with $\Delta G=+3.56 \mathrm{kJ} / \mathrm{mol}$ ?
(a) $\mathrm{A} \rightarrow \mathrm{B}, \Delta G=+6.08 \mathrm{k} / \mathrm{mol}$
(b) $C \rightarrow D, \Delta G=+3.56 \mathrm{kJ} / \mathrm{mol}$
(c) $E \rightarrow F, \Delta G=0 \mathrm{k} / \mathrm{mol}$
(d) $G \rightarrow H, \Delta G=-1.22 \mathrm{kJ} / \mathrm{mol}$
(e) $1 \rightarrow 1, \Delta G=-5.91 \mathrm{kJ} / \mathrm{mol}$

Key Concepts

Additivity of ?G Values

When reactions are coupled, the total free energy change is the sum of the individual ?G values. For the overall process to be spontaneous, the combined ?G must be negative. This principle allows scientists to evaluate which reactions can feasibly drive others, based on their energy profiles.

Exergonic Reaction

An exergonic reaction has a negative ?G, meaning that it releases free energy during the reaction. This release of energy can be harnessed to drive other non-spontaneous reactions when the two processes are coupled together.

Endergonic Reaction

An endergonic reaction is characterized by a positive ?G, meaning it absorbs energy from its surroundings. Such reactions do not occur spontaneously unless they are coupled with another reaction that supplies the necessary free energy.

Free Energy (?G) and Reaction Spontaneity

The Gibbs free energy change (?G) of a reaction assesses its spontaneity under constant temperature and pressure. A negative ?G indicates that a reaction can occur spontaneously because it releases free energy, whereas a positive ?G signifies that the reaction is non-spontaneous and requires energy input.

Reaction Coupling

Reaction coupling involves linking an energetically unfavorable (endergonic) reaction with a favorable (exergonic) reaction so that the energy released by the exergonic process drives the endergonic one. This concept is fundamental in biochemistry and thermodynamics, as it allows cells to perform work that would otherwise be energetically prohibitive.

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