Free energy, also known as Gibbs free energy, is a thermodynamic quantity that measures the amount of energy available to do work in a system at a constant temperature and pressure.
The change in free energy of a system, represented by the symbol ΔG, determines whether a reaction or process will occur spontaneously. A negative ΔG indicates that the reaction or process is spontaneous, while a positive ΔG means that it is non-spontaneous.
The equation for calculating free energy is ΔG = ΔH - TΔS, where ΔH is the change in enthalpy (heat) of the system, T is the temperature in Kelvin, and ΔS is the change in entropy (disorder) of the system.
Free energy allows us to predict the direction and spontaneity of chemical reactions. Reactions with a negative ΔG are thermodynamically favorable and will proceed spontaneously, while those with a positive ΔG require an input of energy to occur.
Free energy is affected by temperature and pressure through the ΔH and ΔS terms in the equation. An increase in temperature or a decrease in pressure will result in a larger ΔS, making the reaction more favorable. On the other hand, a decrease in temperature or an increase in pressure will lead to a smaller ΔS, making the reaction less favorable.