Question

Why ethanol & water show positive deviation. Explain in the point of view of chemical bonding.

please explain in detail. Exam tomorrow.

Answer 1

In more generality, Raoult's law is stated as

Pi=xiPvap
and read "the partial vapor pressure of species i is its (pure) vapor pressure multiplied by its mole fraction in the liquid phase." It assumes an ideal-gas gas phase and an ideal-solution liquid phase; an ideal solution is one in which all intermolecular attractions are of equal strength. More explicitly, the a−b interactions are of equal strength to the a−a and b−b interactions, where a and b represent different chemical species in solution.

A positive deviation from Raoult's law occurs when the partial vapor pressure is greater than would be expected from Raoult's law. From a microscopic perspective, this implies that the a−b interactions are weaker than the a−a and b−b interactions.

Here, water forms hydrogen bonds of greater strength and magnitude than does methanol, and one expects that a water-methanol mixture will therefore possess weaker intermolecular interactions than those in a solution of pure water.