Thermochemistry

In chemistry, enthalpy is the amount of heat energy. Reactions can be determined as exothermic or endothermic depending on their enthaply changes: an exothermic reaction that gives out heat has an overall negative enthalpy and an endotheric reaction that takes in heat has an overall positive enthalpy. Enthaply can be determined experimentally by calorimetry or theoritically by calculations such as involving Hess's Law.