Final answer:
The enthalpy change for a process and its reverse are equal in magnitude but opposite in sign, as represented by the equation ΔH = -ΔH. This relationship is a result of enthalpy being a state function and is supported by Hess's law.
Step-by-step explanation:
The enthalpy change for a process and its reverse are related by the equation ΔH = -ΔH. This means that the change in enthalpy for a given process is equal in magnitude but opposite in sign compared to its reverse process. For example, if the enthalpy change for the sublimation of a substance is positive, the enthalpy change for the reverse process, deposition, would be the same numerical value but negative.
This relationship is a consequence of enthalpy being a state function and is illustrated by Hess's law, which posits that the enthalpy change for a total process is the sum of the enthalpy changes for the individual steps, irrespective of the path taken. Sublimation and deposition are examples of phase changes where this principle applies, and enthalpy changes are often calculated using bond energies and standard heats of formation.