5.4 Hess' Law

  • Hess’ Law: the enthalpy change for the conversion of reactants to products is the same whether the conversion occurs in one step or several steps.

    Hess' Law

Rules for Enthalpy Changes

  • If you reverse a chemical reaction, you must also reverse the sign of ΔH.
  • The magnitude of ΔH is directly proportional to the number of moles of reactants and products. If you multiply a balanced equation by a factor, the value of ΔH is multiplied by the same factor.