# Homework Help: Gas temperature from A->B->C

1. Dec 1, 2011

### the_man

1. The problem statement, all variables and given/known data

The task is to get Q, that gas has received through A-B-C change?
Second task is to get usefulness of the machine?

http://img40.imageshack.us/img40/8372/toplinaabc.jpg [Broken]

2. Relevant equations

W=pV

3. The attempt at a solution

If I use W=pV i get 0 from A->B so i cant get usefulness. No idea.

Last edited by a moderator: May 5, 2017
2. Dec 1, 2011

### grzz

To get the heat energy in or out of system one requires the value of the number of moles of gas and the gas constant R or the temperatures at some points on the graph.

3. Dec 1, 2011

### the_man

So from A->B formula is PV=nRT then I get dT=((p2-p1)*v1)/nR?

from B->C formula is W=p2(v2*v1) and with ideal gas dT=(p2(v2-v1))/nR?

But how to get Q from that?

4. Dec 1, 2011

### grzz

from A->B formula is PV=nRT then I get dT=((p2-p1)*v1)/nR ...yes

from B->C formula is W=p2(v2*v1) ...replace * by -

dT=(p2(v2-v1))/nR ...yes

To get the heat transfer one can use $\Delta$U = $\Delta$Q + $\Delta$W where U is the internal energy.

5. Dec 1, 2011

### the_man

okay man, thanks!