What does Gibbs free energy measure?

Gibbs free energy is a thermodynamic potential that measures the maximum reversible work that can be performed by a system at constant temperature and pressure. It is particularly useful in predicting the spontaneity of a reaction. When evaluating the formation of compounds, Gibbs free energy provides insights into whether a reaction can occur under the given conditions.

Option B refers to the energy required for the formation of a compound from its elements and aligns with the concept of Gibbs free energy because if the formation process has a negative Gibbs free energy change, it indicates that the formation is energetically favorable and spontaneous. Conversely, if the Gibbs energy change is positive, the reaction is non-spontaneous under standard conditions.

Other answer choices address different concepts. The energy needed to break a bond pertains more to bond dissociation energy, which does not focus on spontaneity or reaction feasibility as Gibbs free energy does. The total entropy in a thermodynamic system is related to the second law of thermodynamics but does not directly equate to Gibbs free energy, which considers both enthalpy and entropy. Lastly, the energy released during a phase change deals with enthalpy changes during state transitions, rather than the formation of compounds or the conditions of spontaneity that Gibbs free energy assesses.