Standard Rxn enthalpy and standard enthalpy of formation

[James Bui 1D]

Can someone explain to me how standard rxn enthalpy and standard enthalpy of formation work? I get that at 25c diatomic gases can have a mole product, but is it only for diatomic gases and what do these things really do or let us know?

[Justin Shafa 2E]

It's important to understand the meanings behind these terms so when you forget equations, you can use your knowledge of thermochemistry to derive them yourself. The standard enthalpy of formation is a measure of the energy released/consumed when one mole of a substance is created under standard conditions from its pure elements. The reaction enthalpy is the heat given off or taken up for the reaction (which is a state property).