Standard enthalpy change of reaction

The standard enthalpy of reaction (denoted ΔH_r^⊖) is the enthalpy change that occurs in a system when matter is transformed by a given chemical reaction, when all reactants and products are in their standard states.

For a generic chemical reaction

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

${\displaystyle \Delta H_{\mathrm {r} }^{\ominus }=\sum _{B}{v_{B}\Delta H_{\mathrm {f} }^{\ominus }(B)}}$

In this equation, v_B is the stoichiometric number 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.

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