Question

How vapour pressure lowering is related to a rise in boiling point of solution
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Answer 1

Explanation: The temperature at which the vapour pressure of the solvent becomes equal to the atmospheric vapour pressure is called as boiling point . When the vapour pressure of the solvent is lowered by adding solute to the solvent then the temperature required for making the vapour pressure of the solution equal to the atmospheric vapour pressure should be increased. Therefore, the boiling point of the solution increases.

Final Answer:

When the vapour pressure is lowered, the temperature should be increased for making the vapour pressure of the solution equal to the atmospheric vapour pressure so that the solution reaches its boiling point. Therefore, the boiling point of the solution increases.

Answer 2

As the vapour pressure of the solution decreases, the boiling point of the solution rises because:

Boiling point: The boiling point of a liquid is defined as the temperature at which it transforms into a gaseous vapour, with the liquid's atmospheric pressure equal to that of the surrounding atmosphere (1 atm).

Vapour Pressure: The pressure exerted by the solvent in a closed system, with a tendency to depart the liquid phase and evaporate as the temperature rises, is known as the vapour pressure of the solution.

• Solvent and solute are both present in the solution. The lower the temperature required for the solution to boil and equalise with air pressure, the more solvent molecules it contains.
• The solution becomes more concentrated as we add solute to it, and the number of solvent molecules decreases. The vapour pressure exerted by the solution decreases as the number of solvent molecules in the solution decreases, therefore the solution must boil at a higher temperature. As a result, the boiling point of the solution rises as the vapour pressure falls.