Chemistry wizzes...

doc111 said:

lol! I have a master's degree in chemistry and I almost fell right into that trap too. He didn't give enough info to be balancing equations though, and it simply asks for the mass of the exhaust gasses, meaning all of the gasses expelled during combustion. We don't even know what kind of fuel he was using. It just says "petrol" which I was under the impression was diesel but I think it's more of a generic term for any auto fuel. I'm not from the U.K. so I really don't know. lol!

Click to expand...

common now. you have a masters degree but are only thinking about the gasoline itself and not the air mixed with it to provide combustion?
hehe I bet you're thinking a lot more now

fuel/air ratio. i may not have a masters in chemistry, but i know how to tune carburetors...

toastycookies said:

common now. you have a masters degree but are only thinking about the gasoline itself and not the air mixed with it to provide combustion?
hehe I bet you're thinking a lot more now

fuel/air ratio. i may not have a masters in chemistry, but i know how to tune carburetors...

Click to expand...

I agree with you and thought of this but there isn't enough information in the problem to calculate that. Given that there isn't (and the mass of the exhaust wouldn't be 3 times the mass of the fuel) enough information I left this variable out of my answer. I'm not a mechanic so I wouldn't even know how to calculate the air/fuel mixture ratio. If he had given this in the problem it would've been relatively easy to calculate the mass of the exhaust taking into consideration the air/fuel mixture ratio. I honestly think this problem was only being used to make the student think (not overthink) and to illustrate the law of conservation of mass. Of course we could nitpick all day long. What about the carbon deposits left behind on the cylinder heads and in the combustion chamber? They may not add up to much but there is calculable mass there too.

again, I made assumptions when answering the question. i believe i said that in my post.

you are not creating mass, you guys are forgetting that you need 25 molecules of O2 for every 2 molecules of octane, that is where the extra mass is coming from.

UGA said:

again, I made assumptions when answering the question. i believe i said that in my post.

you are not creating mass, you guys are forgetting that you need 25 molecules of O2 for every 2 molecules of octane, that is where the extra mass is coming from.

Click to expand...

There just isn't enough info in the OP to give a good answer IMO. What is "petrol"? What is the air/fuel ratio? Without this information the problem cannot be solved unless these are givens which I'm unaware if they are or not. You are correct though that there should be some gained mass with the air taken into the carburetor. I'm not a mechanic though. lol!