Calculate Heat of Combustion of Graphite

[Hamal_Arietis]

Homework Statement

The heat of combustion of graphite and that of CO is 394kJ/mol and 283 kJ/mol, respectively. When 12g of graphite is combusted incompletely, the same volume of CO and CO2 are generated. Calculate the heat of generated by this combustion. Choose the closet value.(kJ)
A.197 B.253 C.308 D.339 E.505 F.677

Homework Equations

The answer is B.253kJ

The Attempt at a Solution

My idea is:
$C+O2→CO\\ 1 \qquad \qquad 1$ and $ΔH_1=-394kJ/mol$
$CO+O2→CO2\\ 0,5 \qquad \qquad 0,5$ and $ΔH_2=-0,5.283 kJ/mol$
So $ΔH=ΔH_1+ΔH_2=-535,5kJ/mol$
Where is my wrong?
Thanks for helping

 

[Bystander]

Where are my wrong?

The answer is B.253kJ

Wrong.
Ask yourself, "How many moles of carbon have been burned? How many moles of gaseous products have been formed? What is the minimum heat?"

 

[Hamal_Arietis]

How many moles of gaseous products have been formed?

I think 0,5 mol CO and 0,5 mol CO2 are generated and 1 mol C is combusted

 

[Bystander]

I think 0,5 mol CO and 0,5 mol CO2 are generated and 1 mol C is combusted

Correct. And the minimum heat released is what?

 

[Hamal_Arietis]

Correct. And the minimum heat released is what?

I don't know.
$C+O2→CO\\ 1 \qquad \qquad 1$ and $ΔH_1=-394kJ/mol$
$CO+O2→CO2\\ 0,5 \qquad \qquad 0,5$ and $ΔH_2=-0,5.283 kJ/mol$
So $ΔH=ΔH_1+ΔH_2=-535,5kJ/mol$
1 mol of C is combusted and 0,5 mol of CO and CO2 are generated . So the heat is -535,5kJ/mol?

 

[Bystander]

What's half a mol x 394 kJ/mol?

 

[Hamal_Arietis]

What's half a mol x 394 kJ/mol?

197kJ/mol
but 1 mol C is burned, not 0,5 mol. And 1mol CO is generated but 0,5 mol CO is burned and 0,5 mol CO2 is generated.

 

[Bystander]

Yes, and ...