We have dealt mainly with pure fluid properties. Virtually everything in nature is a mixture. Mixture are much more complex than pure fluids. In order to understand mixtures let us define a mixing process which takes place at constant pressure and temperature. Constant temperature is more difficult.
Most mixing processes are either endothermic or exothermic.
To make a mixing process isothermal you need to add or remove heat as the mixing proceeds. You go into the lab and mix 250 ml of CHCl with 250 ml of acetone. Describe what happens, describe the process. The pressure is constant if done in an open container, therefore the volume will change in some way. The process will either give up heat or take in heat, but the heat transfer will probably not be fast enough to keep the process isothermal.