what is enthalpy change
Top 10 amazing movie makeup transformations. Enthalpy is the heat energy exchange that takes place during chemical reactions. It has the symbol H and is measured in kJ/mol, or kilojoules per mole. The energy exchanged with the surrounding environment at constant pressure is called the enthalpy change of a reaction. To measure the change, standard conditions are used, including a pressure of 1 atmosphere and a temperature of 298 Kelvin (77Â°F or 25Â°C).