## Chemistry: The Central Science (13th Edition)

$\Delta H = +90kJ$
The Hess's law states that, if a reaction have two or more steps, like the one in the problem: $A --> B$ $:\Delta H = + 30kJ$ $B --> C$ $: \Delta H = +60kJ$ The entropy can be calculated by the sum of the two steps involved. $\Delta H : A --> C = (+30kJ) + (+60kJ) = +90kJ$