Question

A sample of methane gas of mass 35 g at 250 K and 12.5 atm expands isothermally until its

pressure is 1.5 atm. Determine the change in entropy of the gas.

Answer 1

Hello there.

A sample of methane gas of mass 35 g at 250 K and 12.5 atm expands isothermally until its
pressure is 1.5 atm. Determine the change in entropy of the gas.

35.57 J/K

Answer 2

We are given with
m = 35 g
T1 = 250 K
P1 = 12.5 atm
Isothermal expanstion
T2 = T1 = 250 K
P2 = 1.5 atm

The change in entropy for isothermal expansion of a gas is
ΔS = R ln P1/P2
ΔS = 8.314 ln 12.5/1.5
ΔS = = 17.63 J/mol-K
Since the gas is methane
ΔS = = 17.63 J/mol-K (35 g)(1 mol/16g)
ΔS = = 35.57 J/K