The Gibbs free energy is the energy associated with a chemical reaction that can be used to do work. The free energy of a system is the sum of its enthalpy (H) plus the product of the temperature (Kelvin) and the entropy (S) of the system.
Enthalpy is the measure of the total energy of any thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.
Entropy is a measure of the chaos or "disorder" of a system. Entropy may be termed as the property of a system which measures the degree of disorder or randomness in the system. It is generally expressed by the symbol, S. Entropy like internal energy and enthalpy, is a state function and change in entropy therefore, depends only on the initial and final states of the system.