# Homework Help: Ideal Gas Law

1. Apr 27, 2006

### willydavidjr

The diagram below shows state changes of an ideal gas. The temperature of states (1), (2), (3) are $$T_1[K], T_2[K]$$ and $$T_3[K]$$ respectively. The state change from (1) to (2) is an adiabatic change (not an isothermal change). The state change from (2) to (3) is a change at constant pressure (isobaric change). The state change from (3) to (1) is a change at constant volume (isochoric change).

Question: 1.) Write the size relation between $$T_1, T_2, T_3$$.

2.) Let the quantity of the ideal gas be 1[mol] and let R[J/mol*K] denote the gas constant. Find the work which the gas did on the outside during the state change from (2) to (3).

My idea:
For number 1: If I will write the relation between the 3 Temperatures, I will follow the Ideal gas law PV=nKT. But n and K can be disable because it will act as a constant and it is the same gas used. So am I correct if I say $$T_1 < T_2 < T_3$$. Or it looks like $$T_1 > T_2$$ What do you say?

For number 2:
Is there work done for the gas outside during the state change?

Note: You can view the diagram on this website : http://www.geocities.com/willydavidjr/pvdiagram

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Last edited: Apr 27, 2006
2. Apr 27, 2006

### Tom Mattson

Staff Emeritus
I agree with you that $T_3$ is the biggest one. To correctly order $T_1$ and $T_2$ you should note that for adiabatic processes, $VT^{\alpha}=constant$.

There has to be, because the gas is expanding. What's the definition of work in terms of pressure and volume?

3. Apr 28, 2006

### willydavidjr

Wait a minute Tom Mattson, I think we're wrong. The question number asked about the size relation. Are they talking about the volume or the amount of Temperatures? And on question number two, how can I find the work done(W=PV) if the given only is the number of moles and R constant?Thank you.

4. Apr 28, 2006

### Tom Mattson

Staff Emeritus
Willy,

I have no idea of what the "size relation" is. That term certainly isn't standard. I assumed that you knew what it meant, and so I took your word for it that it was an inequality involving the temperatures. If it is something else then you should say so.

5. Apr 28, 2006

### willydavidjr

Ok thank you, I am sorry because that was the same sentence I have here, maybe its an inequality involving temperatures.

How about "Let the quantity of the ideal gas be 1[mol] and let R[J/mol*K] denote the gas constant. Find the work which the gas did on the outside during the state change from (2) to (3)."?

My problem about this is that the given are n and R. We have no detail for the P,V,T to get the Work=PV....How can I solve it?

6. Apr 28, 2006

### willydavidjr

It seems that T1 and T2 are uqual?