If you need to reverse the following reaction in order for it to be an intermediate reaction in a hess's law problem, what would be the final value for the enthalpy of reaction you use for this intermediate reaction? h2 + 0.5 o2 h2o, h = -286 kj

When reversing a given reaction, we simply change the sign of the standard enthalpy change value. Therefore, the reaction will become:
H₂O → H₂ + 0.5O₂, ΔH = 286kJ
This is because if a certain amount of energy is released when a reaction occurs, the same amount of energy must be supplied for the reaction to occur in the reverse direction.