# Homework Help: Thermodynamic Problem HELP

1. Aug 12, 2009

### Nguyenfa.t

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

The problem is on the attachment. I cant seem to find the volume or temperature of T. If someone can tell me how to find them i can do the rest of the problem. Any help would be greatly appreciated.

2. Relevant equations

3. The attempt at a solution

on the attachment

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2. Aug 12, 2009

### kuruman

You say you can't seem to find the volume or temperature. What have you tried? What equations did you start from?

3. Aug 12, 2009

### Nguyenfa.t

i used the PV= NRT

I cant find the Volume and Temperature of point C only.

4. Aug 12, 2009

### kuruman

I will not be able to offer any suggestions until I can open your attachments.

5. Aug 12, 2009

### Nguyenfa.t

Well the problem is

One mole of a diatomic ideal gas has a pressure of 8atm and a volume of 3 L at point A. The gas is then expanded isothermally to point B where the volume is 12 L. The gas is then compressed isobarically to point C. the gas is returned to point A via an adiabatic compression. Depending on the calculation assume that R is 8 J/Mol (K) or .08 L atm/ mol K

6. Aug 12, 2009

### kuruman

I can see the attachments now. You are given the volume, pressure, number of moles and R. Can you find the temperature at point A?

7. Aug 12, 2009

### Nguyenfa.t

yes i found the temp of A and B because they are the same since they are isothermal. knowing that i could find the Pressure of B and C because they are isobaric, but i cant find the volume or temp of point C.

8. Aug 12, 2009

### kuruman

OK. Now there is an equation that relates point A to point B and one that relates point A to point C. What are these equations?

9. Aug 12, 2009

### Nguyenfa.t

I dont know what equations and how do they relate? by going back to a via adiabatic process doenst that mean no heat is transferred?

10. Aug 12, 2009

### kuruman

Yes, adiabatic means no heat is transferred. Also, for the adiabatic process,

pAVAγ = pCVCγ

where γ = CP/CV

Find γ for a diatomic gas, then use this relation to find VC.

11. Aug 12, 2009

### Nguyenfa.t

so Cp/Cv= 7/2R divided by 5/2R? where R is .08?

12. Aug 12, 2009

### Nguyenfa.t

and then what do i do? can you show me please?

13. Aug 12, 2009

### Nguyenfa.t

i get y= 1.4 then what do i do?

14. Aug 12, 2009

### kuruman

Use the relation I gave you earlier to find VC. You know everything else. Once you have VC, you can find TC.

15. Aug 12, 2009

### Nguyenfa.t

i get Vc^1.4= 42.8 how do i solve that? can anyone else help?

16. Aug 12, 2009

### queenofbabes

Surely you know logarithms?

17. Aug 12, 2009

### Nguyenfa.t

is it ln 42.8= 1.4? but then what do i solve?

18. Aug 13, 2009

### kuruman

You can rewrite 1.4 as 7/5. You get

VC7/5=42.8

Raise both sides of the equation to the 5/7 power. This gives you

(VC7/5)5/7=42.85/7

Can you get a number for VC now?