unit 11: states of matter · unit: states of matter kinetic theory of liquids: v.p. and b.p. ......

Unit: States of Matter

Kinetic Theory of Liquids: V.P. and B.P.

Copyright © 2015 MsRazz ChemClass

Dalton’s law of partial pressures

• Dalton’s law of partial pressures states

that the total pressure of a mixture of

gases is equal to the sum of the pressures

of all the gases of the mixture.

• The portion of total pressure contributed

by a single gas is called its partial

pressure

• The partial pressure of a gas depends on

the number of moles, size of the container,

and temperature and is independent of the

type of gas.

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Ptotal = P1 + P2 + P3 +...Pn

•Partial pressure can be used to

calculate the amount of gas produced

in a chemical reaction



Intramolecular Forces• The prefix Intra means within

• Attractive forces between molecules cause

some materials to be solids, some to be

liquids, and some to be gases at the same

temperature



Intermolecular Forces• The prefix inter means Between or among

• Dispersion forces are weak forces that

result from temporary shifts in density of

electrons in electron clouds.



Dipole-dipole forces are attractions

between oppositely charged

regions of polar molecules



Hydrogen bonds are special dipole-dipole attractions

that occur between molecules that contain a hydrogen

atom bonded to a small, highly electronegative atom

with at least one lone pair of electrons, typically

fluorine, oxygen, or nitrogen.



Vapor Pressure (V.P.)

Vapor pressure (V.P.): The pressure

caused by the evaporated particles in

a closed container.

•With the lid, the vapor will be steady

so the pressure can be measured.

•Without the lid, the particles will

diffuse.



Vapor Pressure

As the IM forces in a liquid

increases, the vapor pressure

decreases.

•As the forces of attraction are

stronger, it is more difficult for

particles to break free.

•There is an indirect relationship.



Vapor Pressure and Temperature

As temperature increases, vapor

pressure will increase.

• This occurs because more particles

have the energy needed to

evaporate.

• There is a direct relationship.



Vapor Pressure

IM forces restrict the movement

of the molecules.

=Stronger attractive

forces (IM forces)

Less evaporation of

particles (less V.P.)



Boiling Point (B.P.)

The temperature at which a

substance will boil.

• Boiling is a conversion from liquid

to gas throughout the entire

substance.

• Recall evaporation is a conversion

from liquid to gas at the surface.



In order to boil:

=Vapor Pressure Atm Pressure



Normal Boiling Point (n.B.P.)

The boiling point at standard

pressure (1 atm)

• If not at sea level, will not see

the n.b.p. (because atm pressure

is different)

The n.B.P. for water is 100°C



Boiling Point (B.P.)

Boiling point is not constant; it

depends on atm pressure!

•Where there is high atm pressure

= B.P. increases

•Where there is low atm pressure

= B.P. decreases



Boiling Point (B.P.)Recall, when a substance is boiling,

temperature remains constant. (In any phase

change, temperature is constant.)

• At the boiling point, the added energy goes

towards the conversion of liquid gas

instead of increasing temperature.

• Boiling can also occur by lowering atm

pressure until it equals the vapor pressure.

(Like in a vacuum!)


Boiling Water at Room Temperature.mp4


Boiling Points for Water at Different

Atm Pressures

n.b.p = 100°C

Sea level 1atm

1.5 atm

0.8 atm

b.p = 90°C

Above Sea level

Takes less energy to

have v.p.=atm pressure.

b.p = 110°C

Below Sea level

Takes more energy to

have v.p.=atm pressure,

so a higher b.p. is

observed here.



Questions?Complete WS 4


unit 11: states of matter · unit: states of matter kinetic theory of liquids: v.p. and b.p. ......

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