Internal combustion engine problem.

[fraggedmemory]

An internal combustion engine runs on octane, the enthalpy of combustion is -5512 kJ/mol. The mass of 1 gallon of fuel is 3 kg.
The engine temperature is 2000 degrees C and the exit temperature is 800 degrees C. What is the work done?

The total enthalpy is -145053 kJ. The total number of moles of octane is 26.3. The molar mass of octane is .1142 kg/mol

I spent a good deal of time on this, and I am not sure how to conceptualize this problem.

*I edited the problem so you don't have to read the poorly written original problem. *

 

[collinsmark]

An internal combustion engine runs on octane, the enthalpy of combustion is -5512 kJ/mol. The mass of 1 gallon of fuel is 3 kg.
The engine temperature is 2000 degrees C and the exit temperature is 800 degrees C. What is the work done?

The total enthalpy is -145053 kJ. The total number of moles of octane is 26.3. The molar mass of octane is .1142 kg/mol

I spent a good deal of time on this, and I am not sure how to conceptualize this problem.

*I edited the problem so you don't have to read the poorly written original problem. *

You've mentioned you've spent a good deal of time on this, so show us what you've come up with so far! We can't help you unless you show us your work.

That said, I think I'd like to see original problem anyway. The way it's written above contains multiple ambiguities. For example, are we dealing with 1 gallon of octane, 3 kg of octane, or some other amount of octane? It can't be both 1 gallon and 3 kg of pure octane, since the density of octane is 0.703 \ \mathrm{gm/cm^3} = 2.661 \ \mathrm{kg/gal}. So the first question is, how much actual ocatane are we dealing with here?

The problem states the "ending" temperature is 800 deg C, but what about the "starting" temperature? Is that the same as the engine temperature? What about pressure? Is the starting pressure the same as the ending pressure?

I think we can assume that the reaction involves oxygen and the byproducts are water and carbon dioxide, but what are the starting temperature and pressure of intake gas?

My point of all this is there seems to be some information left out here and there.