Heat of combustion of methane using bond energies

[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
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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

 

[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.

 

[zeithief]

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

 

[geosonel]

well, your bond energies also do not agree.
see red corrections below:

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[/color]
O==O = 502 KJ/mol 390.2[/color]
C==O = 799 KJ/mol 746.7[/color]
O--H = 464 KJ/mol 438.1[/color]
________________

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