If a reaction is exergonic, what is true about its ΔG?

• A. The ΔG is negative and the reaction releases energy
• B. The ΔG is zero
• C. The ΔG is positive and energy is absorbed
• D. The ΔG can be either sign with no relation to spontaneity

Answer: (B)

An exergonic reaction is characterized by a negative free-energy change. This means the products have lower Gibbs free energy than the reactants, so energy is released to the surroundings as the reaction proceeds. Since ΔG is negative, the process can happen spontaneously under those conditions (though the rate depends on activation energy, not just ΔG).

Zero ΔG would indicate the system is at equilibrium, with no net energy release or absorption and no net change in the overall amounts of reactants and products. Positive ΔG indicates an endergonic, energy-absorbing reaction. The idea that ΔG can be any sign with no relation to spontaneity is incorrect because spontaneity is linked to the sign of ΔG: negative for spontaneous, positive for non-spontaneous, and zero at equilibrium.