The document discusses vapor pressure and boiling points. It explains that vapor pressure increases with temperature as more liquid molecules escape into the gas phase, creating pressure above the liquid. Boiling occurs when vapor pressure equals atmospheric pressure. Boiling point depends on the strength of molecular attractions, with stronger attractions yielding higher boiling points. Boiling points change with pressure, with lower pressure resulting in lower boiling points and higher pressure yielding higher boiling points.

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 itsin equilibrium with its liquidliquid state.state.
 Liquid molecules at the surfaceLiquid molecules at the surface escapeescape into theinto the
gasgas phase.phase.
 These gas particles createThese gas particles create pressurepressure above theabove the
liquidliquid in a closed container.in a closed container.

2.  Vapor PressureVapor Pressure increasesincreases withwith
increasing temperature.increasing temperature.
20o
C 80o
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 anygas at any
temperaturetemperature
 VaporizationVaporization – When a liquid– When a liquid  gas whengas when heatheat
is applied or at theis applied or at the boilingboiling temperaturetemperature
 BoilingBoiling – occurs when the vapor pressure above– occurs when the vapor pressure above
the liquidthe liquid equalsequals the atmospheric pressure.the atmospheric pressure.

4. Normal Boiling PointNormal Boiling Point --
--boiling temperature when pressure is atboiling temperature when pressure is at
1atm1atm oror 760torr.760torr.
 Boiling Point is a physical constant. ItBoiling Point is a physical constant. It
depends on thedepends on the strengthstrength of the attractionof 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 withBoiling 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 attemperatures at highhigh elevations- waterelevations- water
boils atboils at 7676oo
CC on Mt. Everest).on Mt. Everest).
 Higher PressureHigher Pressure == higherhigher boiling pointboiling point
(example = pressure cooker – cooks(example = pressure cooker – cooks
fasterfaster because you cook at abecause you cook at a higherhigher
temperature.)temperature.)

7.  Boiling Points Change withBoiling 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 attemperatures at highhigh elevations- waterelevations- water
boils atboils at 7676oo
CC on Mt. Everest).on Mt. Everest).
 Higher PressureHigher Pressure == higherhigher boiling pointboiling point
(example = pressure cooker – cooks(example = pressure cooker – cooks
fasterfaster because you cook at abecause you cook at a higherhigher
temperature.)temperature.)