# Thermodynamics - Ideal Gas Law

1. Apr 26, 2009

### science.girl

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

A cylinder contains 2 moles of an ideal monatomic gas that is initially at state A with a volume of 1.0 x 10-2 m3 and a pressure of 4.0 x 105 Pa.
The gas is brought isobarically to state B. where the volume is 2.0 x 10-2 m3.
The gas is then brought at constant volume to state C, where its temperature is the same as at state A. The gas is then brought isothermally back to state A.

a. Determine the pressure of the gas at state C.

b. State whether the net work done by the gas during the complete cycle is positive, negative, or zero. Justify your answer.

c. State whether this device is a refrigerator or a heat engine. Justify your answer.

2. Relevant equations
PV = nRT

3. The attempt at a solution

Well, I have points A and B on a PV diagram. I need to figure out the pressure of the gas at state C to proceed.

I know I have to apply the Ideal Gas Law, but I'm just not sure how. Any help?

2. Apr 26, 2009

### NBAJam100

The gas was brought at constant volume to state C correct? So if the gas was brought to C at constant volume, that means it didnt change, so it has to have the same volume as it did in step B.

3. Apr 27, 2009

### Andrew Mason

You have the right equation. What is the temperature at B? (apply ideal gas law). What is the change in temperature in going to C? Apply the ideal gas law again to get the change in pressure from B to C.

AM

4. Apr 27, 2009

### NBAJam100

wow, sorry for my useless post. for some reason i read it as your problem being you werent sure what the volume was at C. Follow Andrews steps.

5. Apr 27, 2009

### science.girl

Thank you for your help, Andrew.