What happens to the value of ΔH for a thermochemical reaction when the reaction is reversed?

Answer 1

The value of ΔH for a thermochemical reaction changes sign when the reaction is reversed. This is because the enthalpy change for the reverse reaction is equal in magnitude but opposite in sign to the forward reaction. For example, if the forward reaction has a ΔH of -100 kJ, the reverse reaction will have a ΔH of +100 kJ.