• 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.
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