Vapour Pressure & Raoult's law Video Lecture | Physical Chemistry

Ans. Vapour pressure is the pressure exerted by the vapour phase of a substance in equilibrium with its liquid or solid phase at a given temperature. It is a measure of the tendency of molecules to escape from the liquid or solid phase and enter the gas phase. Raoult's law states that the partial vapour pressure of each component in an ideal solution is directly proportional to its mole fraction in the solution and the vapour pressure of the pure component. In other words, it describes the behaviour of ideal mixtures where the interactions between the components are negligible.

Ans. According to Raoult's law, the vapour pressure of a component in an ideal solution is directly proportional to its mole fraction in the solution and the vapour pressure of the pure component. As temperature increases, the average kinetic energy of the molecules also increases. This leads to an increase in the number of molecules with enough energy to escape from the liquid phase and enter the gas phase, resulting in an increase in vapour pressure. Therefore, according to Raoult's law, an increase in temperature leads to an increase in vapour pressure.

Ans. Raoult's law serves as a useful approximation in understanding and predicting the behaviour of ideal mixtures. It finds applications in various fields such as chemical engineering, pharmaceuticals, and environmental science. For example, in chemical engineering, Raoult's law is used in the design and optimization of distillation processes, where the separation of different components in a mixture is based on their different vapour pressures. In pharmaceuticals, it helps in understanding the solubility and volatility of drugs in different solvents, aiding in drug formulation and delivery. In environmental science, Raoult's law is applied to study the evaporation of volatile organic compounds from water bodies, which is crucial in assessing air and water pollution.

Ans. Deviations from Raoult's law occur in real solutions when there are significant intermolecular interactions between the components. Two types of deviations can be observed - positive deviations and negative deviations. Positive deviations occur when the intermolecular interactions are stronger between the unlike molecules than between the like molecules. This leads to a higher vapour pressure than predicted by Raoult's law. Negative deviations occur when the intermolecular interactions are weaker between the unlike molecules than between the like molecules. This leads to a lower vapour pressure than predicted by Raoult's law. Deviations from Raoult's law are more common in non-ideal solutions.

Ans. Azeotropes are special mixtures that exhibit constant boiling points and have vapour compositions different from the liquid compositions. These mixtures cannot be separated by simple distillation. Deviations from Raoult's law can be explained by the formation of azeotropes. In the case of positive deviations, when the intermolecular interactions are stronger between the unlike molecules, the mixture forms an azeotrope with a higher boiling point than the boiling points of the individual components. In the case of negative deviations, when the intermolecular interactions are weaker between the unlike molecules, the mixture forms an azeotrope with a lower boiling point than the boiling points of the individual components. Azeotropes play a crucial role in understanding and predicting the behaviour of non-ideal solutions.