3. Consider the addition reaction between propene, C3H6, and chlorine gas, Cl2 that forms 1,2-dichloropropane. Using bond energies, what is the enthalpy change for this reaction?

Answer 1

You didn't provide the bond energies, so looking them up on the internet, I found the following:

C-C 347 kJ/mol

C=C 614 kJ/mol

C-H 413 kJ/mol

C-Cl 339 kJ/mol

The reactant side has

1 C-C bond x 347 kJ/mol = 347 kJ

1 C=C bond x 614 kJ/mol = 614 kJ

6 C-H bonds x 413 kJ.mol = 2478 kJ

1 Cl-Cl bond = 239 kJ/mol = 239 kJ

TOTAL = 3678 kJ

The product, 1,2-dichloropropane has:

2 C-C bonds x 347 kJ/mol = 694 kJ

2 C-Cl bonds x 339 kJ/mol = 678 kJ

6 C-H bonds x 413 kJ/mol = 2478 kJ

TOTAL = 3850 kJ

The difference (∆Hrxn) = -172 kJ (negative because you add energy to break the bonds in the reactants, and you liberate energy in the products when bonds are formed