Final answer:
The free energy change (∆G) reflects the usable energy in a system that is available for doing work, accounting for entropy loss and is used to determine the spontaneity of a reaction and equilibrium composition.
Step-by-step explanation:
The free energy change (∆G) reflects the amount of energy in a system that is available for doing work after accounting for the energy lost to entropy. This concept is named after the American scientist Josiah Gibbs. When a chemical reaction occurs, there is a change in Gibbs free energy, which can be calculated using the formula ∆G = ∆H - T∆S, where ∆H represents the change in enthalpy, T is the absolute temperature in Kelvin, and ∆S is the change in entropy.
It's important to ensure that all units are consistent when performing these calculations, typically resulting in ∆G being expressed in kJ/mol. The change in Gibbs free energy is critical for determining the spontaneity of a reaction and the composition of the system at equilibrium.