(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A thermally insulated cylinder, closed at both ends, is fitted with a frictionless heat-conducting piston that divides the cylinder into two parts. Initially, the piston is clamped in the center with 1 liter of air at 300 K and 2 atm pressure on one side and 1 liter of air at 300K at 1 atm pressure on the other side. The piston is released and reaches equilibrium in pressure and temperature at a new position. Compute the final pressure and temperature and increase of entropy if air is assumed to be the ideal gas. What irreversible process has taken place?

2. Relevant equations

[tex]\Delta[/tex]S = [tex]\Delta[/tex]Q/T

3. The attempt at a solution

This is an isothermal free expansion. So temperature remains constant. I know the final pressure will be 1.5 atm (intuitively, (1+2)/2), but how can I compute this out by ideal gas law?

By PV=nRT,

(101325)(1000/1000000)=n (8.31)(300)

n1(the compartment with 1atm)=0.040643802

n2(the compartment with 2atm) = 0.081828

TOTAL number of moles = 0.12193

When I search through the Internet, I find this equation

[tex]\Delta[/tex]S=nRln(Vf/Vi) = 0.12193(8.31)ln2 = 0.702323.........

but the answer is 0.0566, what's wrong with my calculation???

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Entropy calculation

**Physics Forums | Science Articles, Homework Help, Discussion**