Enthalpy
Enthalpy is a property of a system also referred to as the heat of that system. Heat and temperature are not the same, but they are related by a simple formula. This can be utilized in calorimetry, where the change in temperature is used to calculate the change in enthalpy associated with a chemical reaction. Enthalpy is denoted with the symbol H, and it is measured in joules, J, which is a measure of energy.
Enthalpy, H, is defined as
H = U + pV
Where U is the internal energy of the system, p is the pressure and V is the volume. pV is the same as the work, w. You may recall from the first law of thermodynamics that the change in energy of a system, U, is given by the sum of the heat and the work applied to that system.
Read about the correlation between heat and energy.