How does Hess's law use intermediate reaction to calculate the enthalpy of a desired reaction?

Hess's law states that the total enthalpy change for a reaction is independent of the pathway taken, allowing the calculation of the enthalpy change for a desired reaction by using intermediate reactions. By adding or subtracting the enthalpy changes of known reactions that lead to the desired reaction, the overall enthalpy change can be determined. This method is particularly useful when direct measurement is difficult, as it relies on the principle that the sum of the enthalpy changes of the intermediate steps equals the enthalpy change of the overall process. Thus, Hess's law provides a systematic approach to calculate enthalpy changes using known reaction data.