# Homework Help: Gas law problem (pchem)

1. Sep 13, 2009

### winterwind

1. The problem statement, all variables and given/known data
The following equations of state are occasionally used for approximate calculations on gases: (gas A) pVm = RT(1+b/Vm), (gas B) p(Vm -b) = RT. Assuming that there were gases that actually obeyed these equations of state, would it be possible to liquefy either gas A or B? Would they have a critical temperature? Explain your answer.

2. Relevant equations
I'm thinking it has something to do with maybe the phase diagrams of these gases? Or maybe the compressibility factor. I know the answer is NO, but can someone please explain it to me?

3. The attempt at a solution
See above.

Thanks!

2. Sep 13, 2009

### Staff: Mentor

IMHO you have to check what happens when the pressure goes up and temperature goes down - how does the V behaves. Seems like simple math.

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3. Sep 13, 2009

Hello winterwind.If it were possible to liquify the gases the isothermal PV graphs would have flat portions where P remains constant for a certain range of values of V ,T being below the critical temperature.Along these flat portions the gases are saturated vapours being in dynamic equilibria with their liquids.Look at your two equations ,make P the subject of them and try to work out if there are any conditions for which P can remain constant whilst V changes.

4. Sep 13, 2009

### winterwind

Ok thanks guys. I am still wondering what conditions would allow the gas to liquefy.

If temperature increases, yet pressure stays the same. Volume decreases, yet pressure stays the same. Are these conditions indicative of a gas being able to be liquefied?

If so, how can I prove it mathematically using those equations? Is it necessary for me to graph the isotherms?

5. Sep 14, 2009