Question

State that values of standard states of formation are important because these are

conveniently used to calculate changes in enthalpy, ΔH of many  reactions.  

Answer 1

Enthalpies (or heats) of formation are extremely useful in calculating reaction enthalpies. That is because any reaction can be visualized as taking place via a path in which first all the reactant compounds are converted to elements and then all the elements are converted in the product compounds.