Enthalpy

Enthalpy () is the sum of a thermodynamic system's internal energy and the product of its pressure and volume. It is a state function in thermodynamics used in many measurements in chemical, biological, and physical systems at a constant external pressure, which is conveniently provided by Earth's ambient atmosphere. The pressure–volume term expresses the work W that was done against constant external pressure P_\text{ext} to establish the system's physical dimensions from V_\text{system, initial}=0 to some final volume V_\text{system, final} (as W=P_\text{ext}\Delta V), i.e. to make room for

energy required to convert a liquid substance to a gas

enthalpy

(of compound) change of enthalpy during the formation of 1 mole of the substance from its constituent elements, with all substances in their standard states, and at a pressure of 1 bar (100 kPa)

thermodynamic process with no change in enthalpy

enthalpy of Solution

enthalpy change that occurs in a system when matter is transformed by a given chemical reaction, when all reactants and products are in their standard states

the heat required to change one mole of a substance from solid state to gaseous state

equation for Gibbs free energy of solvation

change in enthalpy during an acid-base reaction

enthalpy change that accompanies the total separation of all atoms in a chemical substance (either a chemical element or a chemical compound

change in enthalpy during the mixture of substances

Principle in physical chemistry