Vapor pressure and boiling

high school chemistry

1. Vapor Pressure and BoilingVapor Pressure and Boiling
Vapor PressureVapor Pressure – the pressure exerted by a – the pressure exerted by a
vaporvapor in equilibrium with its in equilibrium with its liquidliquid state. state.
Liquid molecules at the surface Liquid molecules at the surface escapeescape into the into the
gasgas phase. phase.
These gas particles create These gas particles create pressurepressure above the above the
liquidliquid in a closed container.in a closed container.

2. Vapor Pressure Vapor Pressure increasesincreases with with
increasing temperature.increasing temperature.
20
o
C 80
o
C
•As temperature increases, the amount of vapor
generated by a liquid in a closed container increases.
•This occurs because as the liquid gains kinetic
energy, the molecules can overcome the
intermolecular forces of attraction that are prevalent
in the liquid phase.

3. Evaporation vs BoilingEvaporation vs Boiling
EvaporationEvaporation - when a liquid - when a liquid  gas at any gas at any
temperaturetemperature
VaporizationVaporization – When a liquid – When a liquid  gas when gas when heat heat
is applied or at the is applied or at the boilingboiling temperature temperature
BoilingBoiling – occurs when the vapor pressure above – occurs when the vapor pressure above
the liquid the liquid equalsequals the atmospheric pressure. the atmospheric pressure.

4. Normal Boiling PointNormal Boiling Point - -
--boiling temperature when pressure is at boiling temperature when pressure is at
1atm1atm or or 760torr.760torr.
Boiling Point is a physical constant. It Boiling Point is a physical constant. It
depends on the depends on the strengthstrength of the attraction of the attraction
between molecules.between molecules.
Strong attraction between molecules = Strong attraction between molecules =
higherhigher boiling point.boiling point.
Weaker attraction between molecules = Weaker attraction between molecules =
lowerlower boiling point.boiling point.

5. Vapor Pressure CurvesVapor Pressure Curves
Graph shows how boiling points change
with change in vapor pressure.

6. Boiling Points Change with Boiling Points Change with
pressure changes.pressure changes.
Less pressureLess pressure = = lower boiling pointlower boiling point
(example = water boils at (example = water boils at lowerlower
temperatures at temperatures at highhigh elevations- water elevations- water
boils at boils at 7676
oo
CC on Mt. Everest). on Mt. Everest).
Higher PressureHigher Pressure = = higherhigher boiling point boiling point
(example = pressure cooker – cooks (example = pressure cooker – cooks
fasterfaster because you cook at a because you cook at a higherhigher
temperature.)temperature.)

7. Boiling Points Change with Boiling Points Change with
pressure changes.pressure changes.
Less pressureLess pressure = = lower boiling pointlower boiling point
(example = water boils at (example = water boils at lowerlower
temperatures at temperatures at highhigh elevations- water elevations- water
boils at boils at 7676
oo
CC on Mt. Everest). on Mt. Everest).
Higher PressureHigher Pressure = = higherhigher boiling point boiling point
(example = pressure cooker – cooks (example = pressure cooker – cooks
fasterfaster because you cook at a because you cook at a higherhigher
temperature.)temperature.)