[Tooren]

Having some issues with this.
What is the standard enthalpy of combustion of C2H6 in kj/mol?
H2(g) + 1/2O2(g) --> H2O(l)   ?H0=  –286 kJ
C2H4(g) + H2(g) --> C2H6(g)   ?H0=  –137 kJ
C2H4(g) + 3O2(g) --> 2CO2(g) + 2H2O(l)   ?H0= –1412 kJ

Now, the answer is presumedly -31561 kj.  But I'm getting no where a number that close.

Since C2H6 is combusted, I want the end-result to be:
(2)C2H6 + (7)O2 --> (6)H2O + (4)CO2 (right?)
So I would turn around the 2nd one to:
C2H6(g) --> C2H4(g) + H2(g)
and then:
2 * [C2H6(g) --> C2H4(g) + H2(g) ]

2 * [H2(g) + (1/2)O2 --> H2O(l)]

2 * [C2H4(g) + 3O2(g) --> 2CO2(g) + 2H2O(l)]

as you can see... I won't get anywhere near -30,000 kJ... (3122 kJ)
I must be doing something extremely wrong...

[Mitch]

I got around -3100KJ. The answer provided must be mistaken.

[Tooren]

This is from a practice ACS review, so the options are:

(A) –1275 kJ   (B) –1548 kJ   (C) –31561 kJ (D) +1834 kJ

I do notice, that half of my answer (3122kJ) = 1561 which is part of the C answer.  Could there be an additional condition to take care of at the end?

[Mitch]

I get -1561 KJ now. I forgot they weren't just asking for KJs but KJ/mols.

[dexangeles]

i got -1561 too you sure C is not a typo -31561 has the -1561 in there if you take off the 3

[Mitch]

It probably is a mistake. I've found more then one mistake in those ACS tests.