Barrons SAT Subject Test Chemistry, 13th Edition

Addition yields

This relationship can also be shown schematically as follows:

TIP

Know how to read this type of chart.

Some commonly used standard heats of formation, designated as ΔH^0 f, are

listed in Table in the Tables for Reference section.
An alternative (and easier) method of calculating enthalpies is based on the

concept that ΔH^0 reaction is equal to the difference between the total enthalpy of the

reactants and that of the products. This can be expressed as follows:

Problem

Calculate ΔH^0 reaction for the decomposition of sodium chlorate.

Step 1 Obtain ΔH^0 f for all substances.