3.
5. 34 Consider the piston-cylinder assembly shown below; 250 moles of gas expand isothermally
after the removal of a 10,000-kg block.
(a) What is the internal energy change for the expansion process?
(b) What is the entropy change of the universe for this process?
Assume that the $PvT$ behavior can be described by the van der Waals equation with
$a = 0.5 [Jm^3/mol^2]$; $b = 4 \times 10^{-5} [m^3/mol]$; and that the ideal gas heat capacity has a constant
value of $c_p^{ideal gas} = 35J/(mol K)$.
Weightless, frictionless piston
$P_{atm}$
$A = 0.1 m^2$
$m=10,000$
$kg$
$P_{atm}$
Isothermal expansion
$A = 0.1 m^2$
250 mol of
van der
Waals gas
State 1
0.4 m
State 2