StellarHess’s Law
Sometimes, a reaction has multiple steps, which makes it more difficult to calculate its change in enthalpy. Sometimes, AP Chemistry will give you problems in which there are multiple equations, with each of them having a different enthalpy of reaction, and you will need to solve for the enthalpy of a different reaction.
In this case, you will need to use Hess’s Law, which says that the enthalpy change of an overall process is equal to the sum of the enthalpy changes in each of the individual steps that make up the overall process. Hess’s Law has different rules for manipulating different reactions in order to solve for a final equation.