What is the Gibbs free energy and how does it relate to the spontaneity of reactions?

The Gibbs free energy is the energy available to do work in a system at constant temperature and pressure. It is a measure of the spontaneity of a reaction, indicating whether a reaction will occur spontaneously or not.

The Gibbs free energy equation is ΔG = ΔH - TΔS, where ΔG is the change in Gibbs free energy, ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy. If ΔG is negative, the reaction is spontaneous and will proceed in the forward direction. If ΔG is positive, the reaction is non-spontaneous and will not occur without an external driving force. If ΔG is zero, the reaction is at equilibrium.

The sign of ΔH and ΔS also affect the spontaneity of a reaction. If ΔH is negative and ΔS is positive, the reaction will always be spontaneous. If ΔH is positive and ΔS is negative, the reaction will never be spontaneous. If both ΔH and ΔS are negative, the reaction will be spontaneous at low temperatures but non-spontaneous at high temperatures. If both ΔH and ΔS are positive, the reaction will be non-spontaneous at low temperatures but spontaneous at high temperatures.

In summary, the Gibbs free energy is a measure of the spontaneity of a reaction, indicating whether a reaction will occur spontaneously or not. The sign of ΔG, ΔH, and ΔS determine the spontaneity of a reaction, with negative ΔG indicating a spontaneous reaction.