## Summary:

- Hess s law of heat summation states that if two or more thermochemical equations can be added together to give a final equation, then the heats of reaction can also be added to give a heat of reaction for the final equation.
- The heats of reaction for the individual reactions are added algebraically.
- Any substance that appears in equal quantities as a reactant in one equation and a product in another equation cancels out algebraically.