Question: how does standard enthalpy work?
Answer: The standard enthalpy of reaction (denoted ΔHr⦵) 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. −vA A + −vB B + ... → vP P + vQ Q ... In this equation, vB is the stoichiometric number of entity B.