# Heat of combustion help

1. Jul 3, 2005

### Chocolaty

Determine the heat of combustion of methane (CH4(g)) by writing a balanced equasion 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
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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

2. Jul 4, 2005

### siddharth

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.

3. Jul 4, 2005

### 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?

4. Jul 4, 2005

### geosonel

well, your bond energies also do not agree.
see red corrections below:
check below for details:
http://members.nuvox.net/~on.jwclymer/rq/hoctable.html