Which statement best describes Gibbs free energy?

Which statement best describes Gibbs free energy?

• A. It is the energy of a system available to do work at constant temperature and pressure
• B. It is the total energy of molecules
• C. It measures only enthalpy
• D. It is the temperature of the system

Answer: (A)

Gibbs free energy tells you how much useful energy a system has to do work when temperature and pressure are held constant. It combines heat content and disorder into a single measure: G = H − TS. Because of this, the energy available to perform non-expansion work under those conditions is what Gibbs free energy represents. The total energy of the system (internal energy) includes all forms of energy, not just what can be used to do work at constant T and P. Enthalpy is about heat content at constant pressure, but it doesn’t account for the usable work after accounting for entropy. Temperature itself isn’t energy; it’s a factor that shapes G through the TS term. So the statement that best captures Gibbs free energy is that it’s the energy of a system available to do work at constant temperature and pressure. The sign of its change also tells you whether a process is spontaneous (negative), at equilibrium (zero), or non-spontaneous (positive).

Gibbs free energy tells you how much useful energy a system has to do work when temperature and pressure are held constant. It combines heat content and disorder into a single measure: G = H − TS. Because of this, the energy available to perform non-expansion work under those conditions is what Gibbs free energy represents. The total energy of the system (internal energy) includes all forms of energy, not just what can be used to do work at constant T and P. Enthalpy is about heat content at constant pressure, but it doesn’t account for the usable work after accounting for entropy. Temperature itself isn’t energy; it’s a factor that shapes G through the TS term. So the statement that best captures Gibbs free energy is that it’s the energy of a system available to do work at constant temperature and pressure. The sign of its change also tells you whether a process is spontaneous (negative), at equilibrium (zero), or non-spontaneous (positive).