Question

In melting point experiment, (we use benzoic acid (solid),acetanilide (solid) and we put them in capillary tube and let them heat with thiele tube.)

why  Raoult's law is related to melting point? I think  Raoult's law is only in liquid.

please make me understand.. How solids are interact with each other as liquid?

Answer 1

Dear student

Raoult's law is a law of thermodynamics established by French chemist François-Marie Raoult in 1887. It states that the partial pressure of each component of an ideal mixture of liquids is equal to the vapour pressure of the pure component multiplied by its mole fraction in the mixture. In consequence, the relative lowering of vapour pressure of a dilute solution of nonvolatile solute is equal to the mole fraction of solute in the solution.

Raoult's law is related to melting point . By dissolving a solute in a solvent, the freezing point of the solution is lowered. The reason for this lower freezing point is that when a liquid freezes, the molecules form a pure solid sample of solvent.Really, it's the same reason that a solution's vapor pressure is lowered (and henceboiling point is elevated)

behavior of a liquid or a solid, using the intermolecular force is not usually the best way to proceed. Most of the forces die off far too slowly to consider the force between just two molecules in something as dense as a liquid. Instead one would need to average out the behavior of all the other molecules to determine the effective potential between two particular molecules. While the underlying potential will be the same in liquid or solid, this effective potential will be different in the liquid than it will be in the solid.

At equilibrium, the rate at which the solidor liquid evaporates is equal to the rate that the gas is condensing back to its original form. All solids and liquids have a vapor pressure, and this pressure is constant regardless of how much of the substance is present.

satrated vapour pessure aurve for he pure water soid sarated vapcur pressure curve tor qud vapour empeature

You can use the simplified definition of a single volatile liquid (the solvent) and a non-volatile solute( solid ) . The vapour pressure of a solution of a non-volatile solute is equal to the vapour pressure of the pure solvent at that temperature multiplied by its mole fraction.

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