- The heat content of a chemical system is called the enthalpy (symbol: H)
- The enthalpy change (H) is the amount of heat released or absorbed when a chemical reaction occurs at constant pressure.
- H = H(products) - H(reactants)
- H is specified per mole of substance as in the balanced chemical equation for the reaction
The units are usually given as kJ mol-1 (kJ/mol) or sometimes as kcal mol-1 (kcal/mol)
1 calorie (1 cal) = 4.184 joules (4.184 J)
- Energy changes are measured under standard laboratory conditions (S.L.C.)
25oC (298K) & 101.3kPa (1 atmosphere)