 # How is Gibbs free energy related to enthalpy and entropy?

Gibbs free energy is the energy associated with a chemical reaction that can do useful work. It equals the enthalpy minus the product of the temperature and entropy of the system. G = H – TS Gibbs free energy is the amount of energy left over after a chemical reaction has taken place. Enthalpy (H) is a measure of how much energy is released or absorbed during a chemical reaction. Energy, in the form of heat, is released in an exothermic reaction, and the change in enthalpy is negative, -H. When heat is absorbed in an endothermic reaction, the change in enthalpy is positive, +H.

• Enthalpy is the amount of heat energy transferred (heat absorbed or emitted) in a chemical process under constant pressure.
• Entropy measures the amount of heat dispersed or transferred during a chemical process.
• Gibbs’ energy is the energy available to initiate a chemical process under constant pressure and temperature.
• At constant temperature ΔG = ΔH – TΔS

∆G = Gibbs Free Energy ∆H = Change in Enthalpy T = Temperature in K ∆S = Change in Entropy