This episode explains how to calculate the enthalpy change of a reaction using standard enthalpies of formation, which are values representing the energy required to form one mole of a compound from its elements. The episode introduces the "products minus reactants" formula. It emphasizes a key fact: the enthalpy change of formation for any pure element in its most stable form is zero. This method offers a mathematical way to determine reaction enthalpy without needing to manipulate multiple equations, like Hess’s Law.