# Isothermal compression of monatomic gas ?

#### zaf

Hello forum members

I need some help on H.W problem...just enough reasoning to atleast get started

the question is as follows:
5 moles of a monoatomic ideal gas at an initial volume of .50 m^3 and an initial pressure of 2.0 * 10^5 Pa undergoes an isothermal compression to .20m^3. Find the final pressure ?

so, the temperature is going to be constant , the inital and final volumes and intial pressure is also know, also the total energy (Q)is going to be work done on the gas... which must be negaive... internal energy is conserved ? am i correct so far....how do i solve this ?

Related Introductory Physics Homework Help News on Phys.org

#### Njorl

You're overcomplicating. The energy doesn't figure into it. It is also irrelevant that the gas is monatomic. The problem is much easier than you suspect.

Njorl

#### arcnets

Right Njorl,
all there is to use is the equation of an ideal gas:
pV = nRT.
Since there is initial & final state, it's a system of 2 equations:
I) p1V1 = nRT
II) p2V2 = nRT
Now, T is not given, so you better eliminate it:
I) T = p1V1/nR
II) T = p2V2/nR
Which are clearly equal, so
I = II) p1V1/nR = p2V2/nR
or (nR cancels)
p1V1 = p2V2
And we solve for p2:
p2= p1V1/V2
OK?

#### Njorl

Yes, but I thought it should be left for Zaf to do with just the hint.

Njorl

#### zaf

yes. i understand arcnets... thank you

#### arcnets

Originally posted by Njorl
Yes, but I thought it should be left for Zaf to do with just the hint.

Njorl
Yes, right. Maybe that was a little too much...

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving