The de-phosphorylation of phosphoenolpyruvate (PEP) to form pyruvate has a change in Gibb’s free energy (ΔG) of -61.9 kJ/mol. How would you describe the reaction?

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The question asks us to describe the de-phosphorylation of phosphoenolpyruvate (PEP) to pyruvate, given a ΔG of -61.9 kJ/mol.
Option a: 'Slightly exergonic' would correspond to a small negative ΔG value. Since -61.9 kJ/mol is a substantially large negative number, this description underestimates the magnitude of the energy release.
Option b: 'Slightly endergonic' asserts a positive ΔG (or a very small negative value). A negative ΔG indicates a spontaneous, energy-releasing process, so this option is incorrect both in sign and in implication.
Option c: 'Highly exergonic' conveys a large, favorable release of free energy. The given ΔG of -61.9 kJ/mol is indeed a substantial negative value, indicating a strong tendency to proceed toward products without input of energy, which aligns with the idea of a highly exergonic reaction.
Option d: 'Highly endergonic' would require a strongly positive ΔG, meaning the reaction would be non-spontaneous and energy-consuming. This directly contradicts the negative ΔG provided, making it incorrect.
To connect to the bigger picture, a large negative ΔG like -61.9 kJ/mol suggests the reaction is far from equilibrium and strongly favors product formation under standard conditions, which is characteristic of energetic steps in metabolism such as PEP to pyruvate in glycolysis. Conversely, the options describing slight exergonicity or any endergonicity fail to capture both the sign and the magnitude of the energy change observed here.
Overall, the description that best matches a substantial negative ΔG is the one labeling the reaction as highly exergonic, while the other choices misstate either the direction (end or reverse) or the magnitude of the energy change.

The de-phosphorylation of phosphoenolpyruvate (PEP) to form pyruvate has a change in Gibb’s free energy (ΔG) of -61.9 kJ/mol. How would you describe the reaction?

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