Hess's law question (please help. I'll give 10 points!)?

Question

calculate the C=O bond energy given the following equations.

C (g ) + O2 (s) --> CO2 (g ) (-393 KJ/mol)

C (s ) --> C (g ) --> (+715 KJ/mol)

1/2O2 (g ) --> O (g ) ( +248 KJ/mol)


Please please please explain in the duh-est way possible. Imagine you're talking to an idiot

Thanks :P

Answer 1

I use the bond energies to find the C=O bond energy:

first:
multiplying following reaction by 2 to find the energy of bond O=O energy

1/2O2 (g ) --> O (g ) ( +248 KJ/mol)
► O2 (g ) --> 2O (g ) ( +496 KJ/mol)

H(O=O) - 0 = 496 KJ/mol => ► H(O=O) = 496 KJ/mol

second:
C(s) is stable but in the first reaction C is in gas phase so its energy is involved;

by these informations:
OVERALLY:

DeltaH = the sum of bond energy of reactants - the sum of bond energy of products

Note: CO2 has 2 C=O bons
-393 = 715 + 496 - 2(C=O)

2(C=O) = 1604 =>
► (C=O) = 802 Kj/mol

Answer 2

the second equation is typed wrong i believe.


Add the enthalpies of each equation:
(-393-equation1)+? (fix that up, eq 2) + 2 (<-- this common numerator two gets rid of the fraction) x (-248 (negative because you have to flip this question and have 2O---> O2))

-393+?+2(-248)