Standard molar entropy is defined as the entropy content of one mole of substance within standard conditions. Standard molar entropy is recorded as units of joules per mole kelvin, and, unlike standard enthalies of formation, its values are absolute.
In chemistry, the standard molar entropy of a gas at standard temperature and pressure, more commonly referred to as STP, receives a number of contributions. These include the heat capacity of one mole of a solid at zero kelvin to its melting point, the latent heat fusion of a solid and the latent heat vaporization of a liquid. Phase transitions and chemical reactions are associated with changes in entropy.