Method 2 for Calculating Net Enthalpy

[Caroline C 1G]

When calculating net enthalpy using Method 2 (not Hess's Law), are the bonds of the reactants always broken and the bonds of the products always formed? Or can the bonds of the products be broken and the bonds of the reactants be formed?

[Nancy Dinh 2J]

When calculating net enthalpy using Method 2 (not Hess's Law), are the bonds of the reactants always broken and the bonds of the products always formed? Or can the bonds of the products be broken and the bonds of the reactants be formed?

If you're breaking bonds in the products and forming bonds in the reactants, I think you're essentially just doing the reverse equation of the original one. Don't forget to change the signs for though. If the forward reaction requires energy, the reverse reaction will release energy.

[PeterTran1C]

For standard equations, the reactants contain the molecules where you "break" bonds which are then used to "form" bonds on the product side of the reaction. Like previously stated, if you wished to "break" bonds with the products and "form" bonds with the reactants you would have to reverse the equation and switch the signs where appropriate, since enthalpy changes are state functions.