Enthalpy of Reaction
The heat absorbed or released when a reaction occurs at constant pressure in the molar amounts of the balanced equation.
Formula / equation
ΔH_rxn = ΣΔH_f(products) − ΣΔH_f(reactants)
Unit
kJ/mol
In depth
Reaction enthalpy can be found by direct calorimetry, from tabulated formation enthalpies, from bond energies, or by combining known reactions using Hess's law. Its sign tells whether the reaction is exothermic or endothermic but nothing about spontaneity on its own.
Examples in the real world
The thermite reaction releases about 850 kJ per mole of Fe₂O₃ reduced.