Gibbs free energy (G, also known as Gibbs function, Gibbs energy, or free enthalpy) is named after the American scientist Josiah Willard Gibbs who first introduced the concept. Gibbs free energy measures the maximum amount of useful work that can be obtained from a chemical reaction or process at constant temperature and pressure. It takes into account both the enthalpy (heat) and entropy (disorder) of a system. Gibbs free energy is denoted by the symbol ‘G’. Its value is usually expressed in Joules or Kilojoules.

If the value of G is negative, the reaction is spontaneous and can occur without the input of external energy. If the value of G is positive, the reaction is non-spontaneous and will require an input of external energy to occur. If the value of G is zero, the system is at equilibrium, and there is no net change in the system.

The Gibbs free energy is a valuable tool for predicting the feasibility and direction of chemical reactions and processes. It is commonly used in chemistry, biochemistry, and other fields of science to analyze and design chemical systems.