HChemVaporPressure2017.notebook
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November06,2017
Nov72:39PM
Vapor Pressure and Table H
Aim: Why does water boil at 95°C in Denver, Colorado?
Nov72:39PM
Vapor Pressure: the pressure exerted by gas molecules
(vapor) above the surface of a liquid as it evaporates.
Vapor pressure increases as e vaporation increases.
Two factors that influence the vapor pressure of a substance :
‐Temperature
‐Intermolecular forces of attraction
H
2
O(l)
H
2
O(g)
Vapor
Pressure
Nov72:39PM
Vapor Pressure & Boiling
Increasing temperature causes more evaporation and
an increase in the vapor pressure because more liquid
particles escape as a gas.
The vapor pressure becomes strong enough to overcome the
atmospheric pressure and the liquid boils.
Nov72:39PM
Vapor Pressure & Boiling
Atmospheric pressure ‐ The
pressure pushing down on the
surface of a liquid.
This pressure interferes with
evaporation (liquid particles
can't escape as easily) and
therefore it is more difficult
to boil.
Two ways to get a liquid to boil:
1)Increase the temperature in order to increase the vapor pressure.
2)Decrease the atmospheric pressure until it equals the vapor pressure.
A liquid will only boil when the vapor pressure of the
liquid is equal to the atmospheric pressure.
AtmosphericPressure
