Question

A friend is calculating the energy of reaction for a combustion reaction using bond energies, and the calculations are returning a positive for ?H. What, if anything, has your friend done incorrectly?

A. He or She used the wrong table of bond energies
B. Nothing, a combustion reaction should have a positive ?H
C. He or she may have subtracted the reactants from the products
D. Bond energies don’t apply to combustion reactants and should not be used.

Answer 1

He or she may have subtracted the bond energies for the reactants from the products.

Step-by-step explanation:

Answer 2

He or She used the wrong table of bond energies

Step-by-step explanation:

We know that we obtain the energy of a reaction also known as the enthalpy of reaction from the formula; ΔHo(reaction) = sum of the bond energies of bonds being broken - sum of the bond energies of the bonds being formed.

Combustion is an exothermic reaction for which the value of ΔH is expected to the negative. If ΔH is not negative, then the calculation was not properly done and the wrong values of bond energy were probably used.