Homework Help: An ideal gas, and a block of copper, have equal volume of 0.5m^3

blade_090 · Nov 6, 2011

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

An ideal gas, and a block of copper, have equal volume of 0.5m^3 at 300K and atmospheric pressure. The pressure on both is increased reversibly and isothermally to 5atm.
Find the work done of each if the compressibility of copper is 0.7X10^-6 atm-1

the atmospheric pressure the question said is 1atm???
I understand that i should used the work done formula W = P dV
bt i duno how to link the compressibility with work done

I like Serena · Nov 6, 2011

Re: thermodynamics

Welcome to PF, blade_090!

Yes, (standard) atmospheric pressure is 1 atm.

And yes, work done is dW = P dV.

Do you have a formula for an ideal gas that links pressure to volume (and temperature)?
And what about a formula for compressibility that links pressure to volume (isothermally)?

blade_090 · Nov 6, 2011

Re: thermodynamics

so far what i know about ideal gas equation is
PV = nRT
so i have to find the volume change for the ideal gas
use it on W = P dV and i manage to find work done for ideal gas :)
however i still dun have any clue about work done on copper
and for compressibility:
K = (-1/v)(dV/dP)
im still confused about compressibility of copper....
what is the use of compressibility??

I like Serena · Nov 7, 2011

Re: thermodynamics

You can rewrite it as:
dW = PdV = -K V_o P dP.
Now integrate?

(We can treat V as a constant volume V_o, since it's nearly constant.)

blade_090 · Nov 7, 2011

Re: thermodynamics

ok i got ur point there...
is that any possible that copper has it own pressure beside the atmospheric pressure??
i found the work done from copper..its 0.443J
bt it is different from the standard answer it gave (0.434J)

I like Serena · Nov 7, 2011

Re: thermodynamics

blade_090 said: ↑

ok i got ur point there...
is that any possible that copper has it own pressure beside the atmospheric pressure??
i found the work done from copper..its 0.443J
bt it is different from the standard answer it gave (0.434J)

I'm not sure what you mean with "its own pressure"?

The copper exerts an opposite pressure to the atmospheric pressure.
When the atmospheric pressure is increased, the copper is compressed and as a result gives a greater opposite pressure such that the balance is maintained.

Your results are pretty close...
What did you use for atmospheric pressure?