1. The Kinetic Molecular Theory
States of Matter—Gases, Liquids and Solids

2. The Kinetic Molecular Theory
Literal interpretation: The theory of moving molecules

3. The Kinetic Molecular Theory
Observations to support the theory:
Diffusion in gases and liquids
Movement of substances from an area of high concentration to one of lower concentration
Ability of a gas to spread out and fill a container
Brownian Movement
The observable movement of particles due to collisions
with moving molecules.

4. The Kinetic Molecular Theory
The theory explains these observations
The theory describes the differences between gas, liquids and solids
The theory explains the gas laws

5. The Kinetic Molecular Theory
Major points: Supports the concept of an ideal gas…
An ideal gas is one that perfectly fits all the assumptions of the kinetic-molecular theory.
Do not actually exist—in theory this is how they would behave:

6. The Kinetic Molecular Theory
1. Gases are made of tiny particles far apart relative to
their size:
Volume occupied by the molecules is inconsequential
Volume is mostly space
Explains why gases are compressible

7. The Kinetic Molecular Theory
2. Gas particles are in continuous, rapid, random
motion
As a result there are collisions with other molecules or with the wall of the container
Creates pressure
Increase in temperature increases the movement of the molecules and thus the pressure exerted by the gas

8. The Kinetic Molecular Theory
3. There are no attractive forces between molecules
under normal conditions of temperature and
pressure
Gas molecules are moving too fast
Gas molecules are too far apart
Intermolecular forces are too weak

9. The Kinetic Molecular Theory
4. Collisions between gas particles and between particles and container walls are elastic collisions.
Collisions in which there is no net loss of total kinetic energy
Kinetic energy can be transferred between two particles during collisions
Total kinetic energy remains the same as long as temperature remains the same

10. The Kinetic Molecular Theory
5. All gases at the same temperature have the same average
kinetic energy. The energy is proportional to the
absolute temperature.
Absolute temperature = Kelvin temp scale
Ke = ½ mv2
Ke = the kinetic energy
m = mass
v = the velocity

11. The Kinetic Molecular Theory
1. Gases are made of tiny particles far apart relative to their size 2. Gas particles are in continuous, rapid, random motion 3. There are no attractive forces between molecules under normal conditions of temperature and pressure 4. Collisions between gas particles and between particles and container walls are elastic collisions. 5. All gases at the same temperature have the same average kinetic energy. The energy is proportional to the absolute temperature.

12. The Kinetic Molecular Theory
Applies only to ideal gases
Most gases behave like an ideal gas under normal conditions
Gases with little attraction between molecules…He/H2/N2
Real gases
Deviate from ideal behavior
Due to intermolecular interaction (H2O, NH3)
High pressure
Low temperature

13. The Kinetic Theory and Changes of State
Gases—Attractions are insignificant
Liquids—Attractions are more important leading to a more ordered state
Solids –Attractions are most important with an ordered state

14. Kinetic Molecular Theory and Changes of State
Attractions between particles in strength:
Least London dispersion forces
Dipole-dipole interaction
Hydrogen bonding
Greatest Metallic, Ionic and Covalent network

15. Kinetic Molecular Theory and Changes of State
Changes of state occur with a change in temperature or pressure
Particles of a substance overcome (or succumb) to intermolecular
attraction
Involves energy

16. Kinetic Molecular Theory and Changes of State
Solids, liquids and gases can undergo various changes in processes that are either endothermic or exothermic

17. Kinetic Molecular Theory and Changes of State
Consider the evaporation of a liquid:
Temperature= the average kinetic energy
Some molecules have more kinetic energy than others
These molecules escape and become gas molecules

18. Kinetic Molecular Theory and Changes of State
Evaporation will occur in closed container also except……
As the liquid evaporates the space above starts to fill with gas molecules until it can hold no more
Gas will start to condense.

19. Kinetic Molecular Theory and Changes of State
Eventually the rate of evaporation will equal the rate of condensation
Two processes will occur simultaneously with no net change
State of Equilibrium
Vapor molecules above the liquid will collide with each other and the container………………………and exert a pressure.
Equilibrium vapor pressure!!!

20. Kinetic Molecular Theory and Changes of State
Every liquid has a specific vapor pressure at a given temperature.
Reflection of the strength of the intermolecular bonding between molecules
Vapor pressure also increases with temperature

21. Kinetic Molecular Theory and Changes of State
Equilibrium vapor pressure is (EVP) used to define boiling point, BPt
Boiling point is the temperature at which the equilibrium vapor pressure equals atmospheric pressure

22. Kinetic Molecular Theory and Changes of State
Boiling point of water is 100 oC only at 760mm Hg
When atmospheric pressure is > 760 mm Hg the boiling pt is > 100.
When atom0spheric pressure is <760mm Hg the boiling pt is <100

23. Kinetic Molecular Theory and Changes of State
Boiling requires a continuous supply of energy……..
Water boils at 100oC and the temperature does not change….even though there is a continuous supply of energy…..
Where does the energy go?

24. Kinetic Molecular Theory and Changes of State
Same is true when ice melts……
It melts (or freezes) at 00C
At this temperature there is a state of equilibrium
Temp will not change if both phases are present

25. Kinetic Molecular Theory and Changes of State
Energy is can be added continuously, but the temperature does not change
Energy is used to change the physical state…this requires a lot of energy!!

26. Kinetic Molecular Theory and Changes of State
The amount of heat energy required to melt one mole of a solid at the solid’s melting point is the solid’s molar enthalpy of fusion.
DHf
Energy absorbed represents potential energy
For water it is 6.009kJ/mol
Xj/g =6.009kJ/M x 1M/18g x 1000J/1kJ
= j/g

27. Kinetic Molecular Theory and Changes of State
The amount of heat energy required to vaporize one mole of a liquid at the liquid’s boiling point is the liquid’s molar enthalpy of vaporization.
DHv
Energy absorbed represents potential energy
For water it is 40.79kJ/mol
Xj/g =40.79J/M x 1M/18g x 1000J/1kJ
= 2266 j/g

28. Kinetic Molecular Theory and Changes of State
Compared to other substances these values are very high.
Water has very strong intermolecular bonding
Hydrogen bonds between highly polar molecules

29. Kinetic Molecular Theory and Changes of State
Unique properties of water is related to the hydrogen bond
4-8 molecular groups in liquid water
Hexagonal arrangement in solid
--> Dipole w/ partial +/-
 High boiling pt of
water
 Solid is less dense..Ice
floats

30. Changes of State are Shown in Phase Diagrams
Changes of phase are depicted in phase diagrams
Show the relationship between state of matter, temperature and pressure

31. Changes of State Shown in Phase Diagrams
Phase diagrams define:
Triple point=the T/P conditions at which all three phases coexist
Critical point = Critical temp and press
Critical temp = temp above which the substance cannot exist as a liquid
Critical press= lowest pressure at which the substance can exist as a liquid at the critical temperature

32. Phase Diagram of Water Interesting points
AD—Ice and vapor in equilibrium
AC– Liquid and vapor in equilibrium
AB—Ice and liquid in equilibrium. Note an increase in pressure lowers melting point
nbp=normal boiling pt
mp =melting point
Critial temp =373.99

33. Phase Diagram of Carbon Dioxide
Note the following:
Very different temp and pressure compared to water’s diagram
Liquid is only possible at high pressure
At normal room conditions CO2 only exists as a gas

34. Phase Change vs Temperature change in a single phase
Melting/Fusion
…Molar heat of fusion
6.009 kJ/mol
Vaporizing
Molar hear of vaporization
40.79kJ/mol
Raising the temperature of a homogeneous material
Specific heat

35. Phase Change
How much energy is absorbed when 47g of ice melts? (at STP)
Energy =47g x 1 mol x 6.009kJ
18g mol
= 15.7 kJ

36. Phase Change
How much energy is absorbed when 47g of water vaporizes? (at STP)
Energy =47g x 1 mol x 40.79kJ
18g mol
= 106 kJ (vs 15.7 kJ—gases have a higher energy content)

37. Phase Change
What mass of steam is required to release 4.97 x 105kJ of energy when it condenses?
grams =4.97 x 105kJ x 1mol x 18g
40.79kJ mol
= 2.19 x 105 g

38. Temperature change in a single phase
Specific heat of water , Cp
Definition… the quantity of heat (q) required to raise 1 gram of water 1oC at a constant pressure.
Value will vary for each substance

39. Temperature change in a single phase
Quantity of energy transferred as heat while a temperature change occurs depends on
The nature of the substance
The mass of the material
The size of the temperature change.
Water has a high specific heat
Metals have low specific heat
Units = J/(g x oC)

40. Temperature change in a single phase
Specific heat of water (l) = 4.18 J/goC
Specific heat of water (s) = 2.06
Specific heat of water (g) = 1.87
Specific heat of ethanol (g) = 1.42
Specific heat of ethanol (l) = 2.44
Specific heat of mercury (l) = 0.140
Specific heat of copper (s) = 0.385
Specific heat of lead (s) = 0.129
Specific heat of aluminum (s) = 0.897

41. Solids and the Kinetic Molecular theory
Properties: Dominated by the fact that
Closely packed particles
Relatively fixed positions
Highest intermolecular or interatomic attractions
Properties are
Definite shape and volume
Definite melting point
High density and incompressibility
Low rate of diffusion

42. Solid structure Solids may be crystalline Solids may be amorphous
Crystals in which particles are arranged in a regular repeating pattern
Particles are randomly arranged

43. Solid structure Crystals
Total 3-D arrangement of particles is the crystal structure
CUBIC
BODY CENTERED CUBIC
TETRGONAL
HEXAGONAL
TRIGONAL
MONO

44. 4-Classes of Crytsalline Solids
Ionic --Ions
Hard and Britle
Covalent Network
Network of molecules
Quartz (SiO)
Diamond
Metallic Crystals
Free moving e-
Covalent Molecular Crystals
Weak….
Water, dry ice

45. Amorphous solids
Without shape
No regular pattern
Glasses
Plastics