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why liquid boils when its vapour pressure equals external pressure.

why liquid boils when its vapour pressure equals external pressure.

Grade:12

2 Answers

Harishwar IIT Roorkee
askIITians Faculty 50 Points
9 years ago
A liquid boils at a temperature at which its vapor pressure is equal to the pressure of the gas above it. The lower the pressure of a gas above a liquid, the lower the temperature at which the liquid will boil.

The Macroscopic View

As a liquid is heated, its vapor pressure increases until the vapor pressure equals the pressure of the gas above it.
Bubbles of vaporized liquid (i.e., gas) form within the bulk liquid and then rise to the surface where they burst and release the gas. (At the boiling temperature the vapor inside a bubble has enough pressure to keep the bubble from collapsing.)
In order to form vapor, the molecules of the liquid must overcome the forces of attraction between them.
The temperature of a boiling liquid remains constant, even when more heat is added.

The boiling point of a liquid is the temperature at which its vapor pressure is equal to the pressure of the gas above it.The normal boiling point of a liquid is the temperature at which its vapor pressure is equal to one atmosphere (760 torr).
rohan
12 Points
9 years ago
At the boiling temperature the vapor inside a bubble has enough pressure to keep the bubble from collapsing.
inside bubble the pressure vapour equals its vapour pressure. to prevent it from collapsing the pressure must be more than atmosphric pressure and the pressure of liquid above it.
then the vapour pressure must be more than the atmospheric pressure.

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