Transcript Phase Changes - Tenafly Public Schools

Liquids
Chemistry
Mrs. Coyle
Liquids

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
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Intermolecular attractions hold molecules
of liquids together.
Incompressible, definite volume.
More dense than gases.
Molecules have kinetic energy.
Vaporization

Change of phase from a liquid to a gas
Evaporation

Vaporization occurring at the surface of
the liquid.
Evaporation example: Bromine
Gas
(Vapor)
Liquid
What happens to the rate of
evaporation as the liquid is
heated?
 The rate of evaporation increases.
Evaporation is a cooling process


Why?
The particles with the higher kinetic
energy escape the liquid first.
Boiling
Vaporization occurring beneath the
liquid’s surface.
Evaporation in a Closed Container
Evaporation in a Closed Container
Liquid
 Vapor

When the rate of evaporation equals the
rate of condensation the system is in
Equilibrium
Vapor Pressure

The pressure of the gas that has
evaporated above a liquid.
The vapor pressure increases with
increasing temperature.
Why?
Because the kinetic energy of the liquid
molecules increases and more leave the
liquid and collide with the walls of the
container.
Boiling Point

The temperature at which a liquid boils.
Boiling and External Pressure

When the external pressure is greater
than the vapor pressure of the bubbles in
the liquid the bubbles cannot come to the
surface. Boiling does not happen.
Boiling and External Pressure

When the external pressure is equal to the
vapor pressure of the bubbles in the
liquid, boiling occurs.
Why does water boil at a lower
temperature at high altitudes?

Because the external pressure is lower.
Normal Boiling Point

The boiling point at 1 atm or 101.3kPa