[davie08]

For the following combustion reaction, ΔHcomb = -726KJ

C₂H₅OH +3O₂  2CO₂ + 3H₂O


How many mole of carbon dioxide could be produced along with 7.87 x 10^4 KJ of energy?

[sjb]

For the following combustion reaction, ΔHcomb = -726KJ

C₂H₅OH +3O₂  2CO₂ + 3H₂O


How many mole of carbon dioxide could be produced along with 7.87 x 10^4 KJ of energy?

-726 kJ per what? mole? ml? gram? pound? other? How many aliquots of 726 kJ are there in 7.87 x 10⁴ kJ

[davie08]

This was all it said.

[Borek]

This was all it said.

sjb asks you to try to understand the question. From the wording it is perfectly clear what is the answer to his question, and once you will know it, question becomes pretty straightforward.

[davie08]

Would the setup be like this:

_______KJ x ________g/_________KJ x ___________mol/___________g

[Borek]

Would work, but do you need g for anything?

How many moles of ethanol in the reaction as written?

[davie08]

I'm not sure what the grams would be used for, so there is two moles of CO₂ as written is that what you meant? I'm so lost lol.

[davie08]

for methanol there is one mole but what would that tell me?

[Borek]

You are told that combustion of 1 mole of ethanol (as written in the reaction) produces 726KJ. Use this information to calculate number of moles that have to be used to produce 7.87×10⁴ KJ.

[davie08]

would this be right?

7.87 x 10^4 KJ x 2CO₂ mole/-726KJ

[Borek]

You are so attached to the conversion factors that you are not seeing what it really is about.

You are quite close now, but why do you use 2CO₂ mole/-726KJ as a factor? You are asked to calculate number of moles of ethanol, so if you are insisting on using conversion factor it should combine 1 mole of ethanol with 726 kJ.

Note that the minus sign is a matter of convention - if you will use it blindly you will get a negative number of moles, which is impossible.