Bond enthalpies

Question

Using the provided table of bond enthalpies, calculate the standard reation enthalpy for the following reaction:

Answer 1

CS2(l) + 6H2O2(l) ==> CO2(g) + 2SO2(g) + 6H2O(l)

Look at the bond energies of the reactants:

C-S = 255 x 2 = 510

H-O-O-H = 2 O-H = 2x460 + O-O = 142 = 1060 x 6 = 6372

Total bond energy of reactants = 510 + 6372 = 6882

Look at the bond energies of the products:

2xC=O (2x745) = 1490

O=S=O (2x469) = 938

O-H = 460 x 6 = 2760

Total bond energy of the products = 1490 + 938 + 2760 = 5188

It takes energy to break bonds (reactants) and energy is released when bonds are made (products)

6882 - 5188 = 1694 kJ = ∆Hrxn

This assumes that I used the correct values from your "table" and also that I did the calculations correctly. The method is the important part, and you should go through and make sure all values are correct.

Hopefully Dr. Bob will also add an answer so we can compare.