Hess's Law
Subject:
Notes Enthalpy / Hess?s Law 2/13/13 CH 4(g) + 2O 2(g) ? CO 2(g) + 2H 2 O (g) ?H? rxn =? ?H? rxn = ??H? f products - ??H? f reactants Electron Affinity: Energy change associated with adding electrons to atoms (anions) Ionization Energy: Energy change associated with removing electrons from atoms (cations) Methods for calculating ?H rxn Hess?s Law: if a reaction can be written as the sum of two or more steps the overall enthalpy of reaction is equal to the sums of the enthalpies of reaction for each of the steps A + B ? G + H ? ?H rxn =? A + B ? C + D ? ?H rxn = x KJ C + D ? E + F ? ?H rxn = y KJ E + F ? G + H ? ?H rxn = z KJ +___________ A + B ? G + H ? ?H rxn = x + y + z KJ
