vapor pressure. evaporation u when fastest particles in a sample of liquid escape from the surface...
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Evaporation When fastest particles in a sample of
liquid escape from the surface of the liquid
During evaporation the slower particles are left behind
What happens to the temperature of a liquid as it evaporates?
When first sealed the molecules gradually escape the surface of the liquid
The vapor above the liquid has a pressure
As the molecules build up above the liquid some condense back to a liquid.
Closed Container
Condensation Slower particles of gas feel effects of
intermolecular forces and become liquid
Leaves only the faster particles in the gas
What happens to the temperature of a the gas during condensation?
Rate of Vaporization = Rate of Condensation
Molecules are constantly changing phase “Dynamic”
The total amount of liquid and vapor remains constant “Equilibrium”
Dynamic equilibrium
The pressure of the gas at equilibrium is called the equilibrium vapor pressure
As the temperature goes up, more molecules vaporize
The equilibrium vapor pressure increases as temperature increases
Vapor Pressure Graph Vapor pressure can be plotted vs the
temperature The curve obtained is the equilibrium
vapor pressure Since different substances all
evaporate at different rates when heat is added, they all have different curves
Boiling A liquid boils when the vapor
pressure = the external pressure Vapor pressure great enough to form
a bubble in the liquid Normal Boiling point is the
temperature a substance boils at 1 atm pressure.
The temperature of a liquid can never rise above it’s boiling point.
Changing the Boiling Point Lower the pressure (going up into
the mountains). Lower external pressure requires
lower vapor pressure Lower vapor pressure means lower
boiling point. Food cooks slower.
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