What is the relationship between Gibbs energy and enthalpy at constant temperature and pressure?

The relationship between Gibbs energy (G) and enthalpy (H) at constant temperature (T) and pressure (P) is given by the equation G = H - TS. This equation indicates that the Gibbs energy is derived from the enthalpy minus the product of temperature and entropy (S).

This relationship is significant in thermodynamics because it allows us to predict the spontaneity of a process. If the change in Gibbs energy (ΔG) for a reaction or process at constant temperature and pressure is negative, then the process is spontaneous. The term TS represents the energy that cannot be used to do work, as it is associated with the disorder or randomness of the system (entropy). Therefore, Gibbs energy combines both enthalpic and entropic contributions, providing a comprehensive picture of the thermodynamic feasibility of processes at constant temperature and pressure.

The other options do not accurately reflect the relationship between Gibbs energy and enthalpy. The equation provided in the correct answer captures the essential interplay between enthalpy, temperature, and entropy, distinguishing it as the appropriate choice.