Final answer:
A constant pressure distillation system is preferable to an isothermal one as it allows heat to be used for both internal energy increase and work on the surroundings, making the process more efficient and simpler to operate.
Step-by-step explanation:
A constant pressure distillation system is preferable to an isothermal distillation system for several reasons. In isothermal processes, which must be conducted slowly to maintain a constant temperature, the heat flow into the system needs to be carefully controlled to prevent temperature changes. This constraint necessitates slow changes of thermodynamic variables to maintain thermal equilibrium, which can be less efficient than processes running at constant pressure.
On the other hand, in a constant pressure distillation system, the heat can be transferred into work on the surroundings and into the internal energy of the substance being distilled. Since Cp, the heat capacity at constant pressure, is typically greater than Cv, the heat capacity at constant volume, a constant pressure system allows for work to be performed by the system on the surroundings. This contributes to an efficient separation process because the heat supplied at constant pressure can be used not only to increase the internal energy but also to do work on the mixture, promoting vaporization.
Furthermore, a constant pressure system allows for a more straightforward operation because the pressure can be maintained by simpler means than controlling temperature, such as a pressure-regulating valve. This simplifies the distillation apparatus and can yield more consistent results in the separation of components based on differences in vapor pressures as described by Raoult's law.