enthalpy A thermodynamic property of a substance given by, H = U + pV, where U is the internal energy, p is the pressure, and V is the volume. For any process that occurs at constant pressure the heat absorbed or evolved is equalt to the enthalpy change if the only work is pressure/volume work, i.e. ΔH = ΔU + pΔV for a process of constant pressure. In chemical reactions the enthalpy change (ΔH) is related to the changes in Gibbs free energy (ΔG) and entropy (ΔS) by the equation ΔG = ΔH - TΔS. Enthalpy is usually expressed in units of kilojoules per mole. Related category • HEAT AND THERMODYNAMICS Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) |