Final answer:
Water and cyclohexene distill together due to their differing boiling points, with fractional distillation separating them based on volatility. The separation is more driven by entropy than by enthalpy changes if the liquids are structurally similar and have similar intermolecular forces.
Step-by-step explanation:
When water and cyclohexene distill together during the distillation process, it's due to their differing boiling points. The process of fractional distillation takes advantage of these differences to separate components in a mixture. The volatility of the substances dictates the order in which they evaporate and condense; the more volatile component (often with a lower boiling point) will distill off first. If the two liquids have sufficiently close boiling points or form an azeotrope, they may distill together as a mixture.
For example, when separating mixtures of hydrocarbons or alcohols, such as a mixture of pentane and hexane, the distillation will occur smoothly without a significant change in energy, as the intermolecular forces between the molecules are quite similar. Therefore, the separation is driven more by entropy, which favors increased disorder in the system, rather than by a substantial change in enthalpy.