How is the enthalpy of reaction related to the enthalpies of formation for the products and reactants?

Explanation:

The enthalpy of reaction is the change of enthalpy of the chemical reaction. It is equal to the heat released or absorbed during the chemical reaction.

The enthalpy of reaction is equal to the difference of the enthalpy at the end of the reaction and the enthalpy at the begining of the reaction.

Since the substances at the end are the products, and the substances at the begining are the reactants, this is equivalent to say that the enthalpy of reaction is equal to the enthalpy of formation for the products less the enthalpy of formation for the reactants.

In the form of equation that is:

"the periodic table is arranged in order of atomic number."