CHEM 121

Chapter 7

Winter 2014

1

Kinetic Molecular Theory of Matter

Explains matter in various states

1. 2.

3.

4. 5.

2

States of Matter

Matter:

Physical states:

•

•

•

3

Properties of Matter:

•

•

•

•

Solids• Strong attractive forces ( )•

Properties:

• _________________ density

• _________________ compressibility

• _________________ shape

• _________________ thermal expansion

4

Liquids• Medium forces ( )•

Properties:

• _________________ density

• _________________ compressibility

• _________________ shape

• _________________ thermal expansion

5

Gases

• No attractive forces• High kinetic E:

Properties:

• _________________ density

• _________________ compressibility

• _________________ shape

• _________________ thermal expansion6

Measuring Pressure

Pressure (P)

http://encarta.msn.com/media_461532488_761573986_1_1/mercury_barometer.html

Barometer:

7

Units of Pressure

• pascal• •

• atmosphere•

• Millimeter of mercury• •

• psi, pounds per square inch (engineering)

mmHg 760 atm 1

8

Gas Laws

9

4 Variables:

P:

T:

V:

n:

•

Boyle’s Law

volume occupied by a gas is __________ related to its pressure

10

A sample of gas has a volume of 100.0 mL at 1.0 atm. If we increase the pressure to 2.0 atm, what is the new volume of the gas (T is constant)?

11

3-minute practice

Charles’s Lawvolume of a gas is __________ related to its temperature

(K)

12

A sample of gas has a volume of 100.0 mL at 27 ˚C. If we heat the gas to 54 ˚C (keeping P constant), what is the new volume of the gas?

13

3-minute practice

Gay-Lussac’s Law

At constant volume, pressure is __________ related to temperature

Combined Gas Law:

14

Avogadro’s LawThe volume occupied by a gas is __________

proportional to the amount (mol) of gas(fixed T & P)

At fixed T & P:equal volumes of any ideal gas have…• •

15

Gas Behavior at STP• STP:

•

•

• Standard Molar Volume

16

What is the volume (mL) of 0.10 g of helium gas at STP?

17

3-minute practice

Ideal Gas LawCombine:

– Boyle’s Law

– Charles’s Law

– Avogadro’s Law

Solve at STP…

18

A tank filled with methane at 23 ˚C and 0.991 atm is fitted with a safety valve that opens if internal pressure exceeds 1.00 x 103 torr. When the tank is placed in boiling water at exactly 100. ˚C, will the safety valve open?

Initial:T =P =n =V =

Final:T =P =n =V =

19

A sample of gas occupies 105 mL at 0.903 atm. If temperature remains constant, what is the volume (in L) at 26.4 kPa?

Initial:P =V =n =

T =

Final:P =V =n =T =

20

Each gas in a mixture acts like it is the only gas present

Dalton’s Law of Partial Pressures:

Mixtures of Gases

Example: When water vapor added to pure air….

Each gas exerts __________________________________

21

Graham’s Law

• Effusion: gas leak through hole

• Diffusion: spontaneous mixing of gases

22

B

A

rate

rate

A massmolecular

B massmolecular

Which will deflate more quickly:

a balloon filled with helium or nitrogen?

23

3-minute practice

Changes of State

24

Intermolecular Forces:

• dipole-dipole• polar molecules

acting like magnets

• if between H andN, O, or F

_______________

O

Intermolecular Forces

25

H

H OH

H

OH

H

• London Dispersion forces• •

Vapor PressureAs a liquid evaporates:

• • • But if closed container…

26

Vapor Pressure:

Boiling• As you increase T, vapor pressure _____________• If vapor pressure reaches atmospheric pressure…

27

Sublimation and Melting

Solids have vapor pressures too!– Typically low or high?

Sublimation:

Melting:

Decomposition:

28

Heating and Cooling Curves

• Plateaus: • Slopes:

29

Specific Heat (SH)Amount of heat to raise the T of ___ of a substance by

____

30

How much energy is needed to raise the temperature of 20.0 g of iron by 14.5 °C?

Changes of State Equations• Heat of Fusion:

•

• Heat of fusion for water = 80 cal / g

• Heat of Vaporization:

•

• Heat of vaporization for water = 540 cal / g

31

Solid State

32

Solid State

33