A 1.00-mole sample of an ideal gas in a vessel with a movable piston initially occupies a

Question:

A 1.00-mole sample of an ideal gas in a vessel with a movable piston initially occupies a volume of 5.00 L at an external pressure of 5.00 atm.
a. If Pex is suddenly lowered to 2.00 atm and the gas is allowed to expand isothermally, calculate the following quantities for the system: ΔE, ΔH, ΔS, ΔG, w, and q.
b. Show by the second law that this process will occur spontaneously.