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The Kinetic Molecular Theory

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States of Matter Gases, Liquids and Solids Phase Change vs Temperature change in a single phase Melting/Fusion Molar heat of fusion 6.009 kJ/mol Vaporizing Molar ... – PowerPoint PPT presentation

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Title: The Kinetic Molecular Theory


1
The Kinetic Molecular Theory
  • States of MatterGases, 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 existin 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
    moleculesHe/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
  • GasesAttractions are insignificant
  • LiquidsAttractions 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 containerand
    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 gt 760 mm Hg the
    boiling pt is gt 100.
  • When atom0spheric pressure is lt760mm Hg the
    boiling pt is lt100

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 statethis
    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 solids melting point is
    the solids 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
  • 333.8 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 liquids boiling
    point is the liquids 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
  • --gt 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 pointthe 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
  • ADIce and vapor in equilibrium
  • AC Liquid and vapor in equilibrium
  • ABIce and liquid in equilibrium. Note an
    increase in pressure lowers melting point
  • nbpnormal 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
    waters 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 1 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 1 mol
  • 106 kJ (vs 15.7 kJgases 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 1 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

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