# Heat of combustion help

Chocolaty
Determine the heat of combustion of methane (CH4(g)) by writing a balanced equation and using the bond energies indicated below.

C--H = 414 KJ/mol
O==O = 502 KJ/mol
C==O = 799 KJ/mol
O--H = 464 KJ/mol
________________

I've googled it and apparently the answer is -890 KJ/mol but when I calculate it it gives me -794 KJ/mol. I must be doing something wrong :S

Homework Helper
Gold Member
I'm getting -794 KJ/mol as well. You googled the experimental value of the Heat of Combustion of methane? Maybe the difference is because the bond energies used are not fully accurate.

zeithief
$$CH_4 + 2O_2 -> CO_2 + 2H_2O$$
change in energy content = $$2*799 + 2*2*464 - (4*414 + 2*502) = -794KJ/mol$$
:rofl: same
any1 to point out what's wrong?

geosonel
well, your bond energies also do not agree.
see red corrections below:
Chocolaty said:
Determine the heat of combustion of methane (CH4(g)) by writing a balanced equation and using the bond energies indicated below.

C--H = 414 KJ/mol 415.2
O==O = 502 KJ/mol 390.2
C==O = 799 KJ/mol 746.7
O--H = 464 KJ/mol 438.1
________________

I've googled it and apparently the answer is -890 KJ/mol but when I calculate it it gives me -794 KJ/mol. I must be doing something wrong :S
check below for details:
http://members.nuvox.net/~on.jwclymer/rq/hoctable.html [Broken]

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