Calculate the value of AH° for the reaction C2H6 + 2 Cl2 - C2H4Cl2 + 2 HCl given the bond energies (kJ/mol):
Bond
Bond Energy
432 kJ/mol H-H
C-H 314 kJ/mol
H-CI 427 kJ/mol
C-C 347 kJ/mol
Cl-Cl 243 kJ/mol
339 kJ/mol C-Cl

In exothermic reactions, the products have less enthalpy than the reactants, and as a result, an exothermic reaction is said to have a negative enthalpy of reaction. This means that the energy required to break the bonds in the reactants is less than the energy released when new bonds form in the products.