Consider two ideal gases, A and B, that are initially separated. For each of the following processes, the gases are allowed to mix. Determine if the entropy change of the system is positive, negative, or zero. Explain.

(a) The process occurs isothermally, at constant P.

(b) The process occurs adiabatically, at constant P.

(c) The process occurs isothermally, at constant V.

(d) The process occurs adiabatically, at constant V.