Dissolution of KOH, ΔHsoln: KOH(s) → KOH(aq) (10.1)
Neutralization of solid KOH, ΔHneut:

KOH(s) + HCl(aq) → H2O(l) + KCl(aq) (10.2)

1) Using Hess's law, show how to combine Reaction 10.1 and Reaction 10.2 to give
KOH(aq) + HCl(aq) → H2O(l) + KCl(aq) (10.3)

2)How should ΔHsoln and ΔHneut be combined (mathematically) to give the change in enthalpy for Reaction 10.3, ΔH?

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.