Question

Which of the following statement is correct?

• A. At a particular temperature, when vapour pressure of a liquid is less than that of atmospheric pressure, boiling point is reached.
• B. Higher the vapour pressure of the liquid at a particular temperature , lower is the boiling point.
• C. All of the above.
• D. Higher the vapour pressure at a particular temperature, lesser the tendency for the molecules to escape easily from the surface

Answer 1

The correct option is B Higher the vapour pressure of the liquid at a particular temperature , lower is the boiling point.

Consider water to be exposed to atmosphere.
Atmospheric pressure is exerted on the surface of the liquid. Collision of atmospheric gases with the liquid surface occurs.
On increasing temperature, when the vapour pressure increases, it pushes the air molecules above the surface, making it easier for the liquid molecules to spread and form vapour. Liquid start boiling when the vapour pressure becomes equal to the atmospheric pressure.
Thus,
At a particular temperature,
When vapour Pressure is equal to atmospheric pressure, boiling point is reached.

1. If a liquid has a high vapour pressure at a particular temperature, it means that its molecules can escape easily from the surface
2. The liquid with the higher vapour pressure at a particular temperature is the one with the lower boiling point.