NSTSE (National Science Talent Search Exam- Unified Council) Class 9: Questions 1 of 2000




If atmospheric pressure decreases the boiling point of a liquid ________


Choice (4) Response
a. Increases
b. Remains same
c. Cannot say
d. Decrease




Reason: Boiling point is the point at which vapor pressure equals atmospheric pressure.

In a liquid, some particles always have enough energy to escape to the gas phase. Gaseous particles are also returning to the liquid.

The vapour pressure is the pressure exerted by the gas when the amount of articles leaving the liquid equals the amount of particles entering the liquid. Because the atmospheric pressure is lower, the vapour pressure of the liquid needs to be lower to reach boiling point. Therefore, less heat is required to make the vapor pressure equal to the atmospheric pressure. The boiling point is lower at higher altitude.