Hess's Law





Hess's Law is used to predict ?H?r in enthalpy changes.

Addition of chemical equations can lead to a net equation. If energy is
included for each equation and added, the result will be the energy for the
net equation.

 Hess's Law says that heat of enthalpy are additive.
 ?H(net) = ??H(r), equals the sum of enthalpies of reaction.
 Two rules:
 * If the chemical equation is reversed, the sign of ?H changes.
 * If coefficients are multiplied, multiply ?H by the same amount.