Question on free expansion:

3 moles of an ideal gas undergo an expansion from a volume of 20 liters to a volume of 30 litres (1L = 0.001 m^3 ). The temperature of the initial and final states are both 20◦C.

(a) Calculate the entropy change of the gas if this process is a reversible isothermal expansion

(b) Calculate the entropy change of the universe if this process is a reversible isothermal expansion

(c) Calculate the entropy change of the gas if this process is an irreversible free expansion

(d) Calculate the entropy change of the universe if this process is an irreversible free expansion.