Standard enthalpy of reaction

The standard enthalpy of reaction (denoted Δ_rH^⊖) is the enthalpy change that occurs in a system when one mole of matter is transformed by a chemical reaction under standard conditions.

For a generic chemical reaction

−v_A A + −v_B B + ... → v_P P + v_Q Q ...

the standard enthalpy of reaction Δ_rH^⊖ is related to the standard enthalpy of formation Δ_fH^o of the reactants and products by the following equation:

$\Delta_\mathrm{r}H^\ominus = \sum_{B}{v_B\Delta_\mathrm{f}H^\ominus(B)}$

In this equation, v_B is the stoichiometric coefficient of entity B.

A similar enthalpy change is the standard enthalpy of formation, which has been determined for a vast number of substances. The enthalpy change of any reaction under any conditions can be computed, given the standard enthalpy of formation of the reactants and products.