What is the heat of formation for an element?

The heat of formation of an element in its standard state is defined as zero. This is based on the principle that the formation enthalpy is a measure of the energy change when one mole of a substance is formed from its constituent elements in their standard states.

Since an element in its standard state does not need to undergo any transformation to form itself, the heat of formation is considered to be zero by convention. This establishes a reference point from which the heats of formation of compounds can be measured.

This concept is essential in thermodynamics and reaction stoichiometry, where it allows for the calculation of the overall change in enthalpy during chemical reactions by referencing the enthalpies of the reactants and products involved.