Kinetic Molecular Theory of Matter




I.  Kinetic Theory of Matter
    -- theory that explains the effects of temperature and pressure on matter
    A.  3 Postulates
          1.  All matter is made up of tiny particles.
          2.  These particles are in constant motion.
          3.  Collisions between these particles are perfectly elastic.

    B.  Four States of Matter
          1.  Solid
          2.  Liquid
          3.  Gas
          4.  Plasma

II.  Gases
      A.  Distinguishing Properties of Gases
           1.  Gases have no definite shape and no definite volume.  They take the shape of their container.
           2.  Particles move very rapidly in gases.
           3.  Gases have lower densities thatn solids or liquids because the particles are not as close together.
           4.   Gases can be compressed because there is alot of space between the particles.
           5.   They expand when heated.

      B.   Gas Pressure
            1.  A gas exerts a pressure on its container because the gas molecules are constantly colliding with the walls of the container.
                Each collision exerts a force on the walls of the container.
            2. Atmospheric pressure is the pressure that the gases in our atmosphere exert on everything on earth.
                Atmospheric pressure is equal to:
                a.  101.325 kPa
                b.  1 atm
                c.  760 mm Hg
                d.  760 torr
                e.  760 millibars
                f.  14.7 lbs/in2
            3.  Manometer - an instrument used to measure gas pressure.
                  There are two kinds of manometers:
                  a.  open arm  manometer
                  b.  closed arm manometer (also known as a barometer)
            4.  Converting Units of Pressure

                 a.  1.5 atm to kPa

                      1.5 atm|101.325 kPa     =     151.95 kPa
                                   |  1 atm
 

                b.  1.5 atm  to  mm Hg

                   1.5 atm|760 mm Hg     =     1140 mm Hg
                                |  1 atm

            5.  Manometer Problems
                a.  Closed Arm Manometers (barometers)
                     -- These are easier than open arm problems
 
                        First, find the difference in the level of Hg.
                        Then, convert from mm Hg to kPa.
                        That's all there is to it.

                        Example:  In a closed manometer, the difference between the two mercury levels is 105 mm.  What is the pressure
                                         of the gas?

                        105 mm Hg| 101.325 kPa    =         14.0 kPa
                                           |   760 mm Hg
 
                b.  Open Arm Manometers
                     -- Because these are open to the atmosphere, you must take atmospheric pressure into account.
 
                     First, find the difference in the level of Hg.
                    Then, convert from mm Hg to kPa.
                    Then subtract this from the atmospheric pressure.

                    Example:  An open manometer is filled with mercury.  The difference in the mercury levels in the two arms is
                                      6 mm.  What is the total pressure, in kilopascals, of the gas in the container if the atmospheric
                                      pressure is 101.3 kPa?

                                      6 mm Hg| 101.325 kPa     =    0.8 kPa
                                                      |  760 mm Hg

                                    101.3 kPa  -  0.8 kPa  =   100.5 kPa
 
    C.  Motion and Physical States
         1. Temperature - a measure of the average kinetic energy of the particles in a substance.
         2.  Kinetic Energy - energy an object posses because of its motion.  KE  =  1/2 mv2 where m = mass and v = velocity
         3. absolute zero  - the temperature at which all molecular motion stops.  Absolute Zero =  -273 oC  or  0 K
         4.  Converting from Celsius to Kelvin

                K  =  oC    +     273

         5.  Energy always flows from an object of higher temperature to one of lower temperature until they both reach the same temperature.
         6. Heat is the amount of energy transferred from a warmer object to a cooler object.  Heat is measured in Joules.

III.  Distinguishing Properties of Liquids
        A.  Liquids have definite volume and definite shape.
        B.  Particles slide past one another.
        C.  Generally liquids are less dense than solids.  (Solid water and Liquid water are exceptions)
        D.  Liquids are less compressible than gases.
        E.  Liquids are viscous.
             1.  Viscosity is the internal friction of a liquid.  We also say that it is the liquid's resistance to flow.
             2.  High Molecular Weight  -  High Viscosity
             3.  Low Molecular Weight  -  Low Viscosity

        F.  Surface Tension - contractive force along  the surface of a liquid.
                                              Example:  This is why some insects can walk on water.
                                              Example:  Soap decreases surface tension.
        G.  Vapor Pressure  -   pressure exerted by the molecules of a confined vapor
        H.  Heat (Enthapy) of Vaporization:  total heat or energy required to evaporate a liquid.
        I.  Normal Boiling Point:  the temperature at which the vapor pressure is equal to the standard atmospheric pressure (101.325 kPa).
        J.  Difference between Boiling and Evaporation:
            1.  Evaporation:  entirely a suface effect that can occur at any temperature (liquid to gas)
            2.  Boiling:  bubbles form at the bottom of a liquid and rise to the top. (liquid to gas)  It can only take place at certain
                                temperatures and pressures.
        K.  Hydrogen Bonding in Water
              1.   Compounds containing hydrogen bonded to N, O, or F are very polar and form hydrogen bonds.
                    Hydrogen Bonds are not as strong as an actual chemical bond but it can hold the two molecules firmly together.
              2.   Ice is less dense than liquid water.  This is because water expands when it freezes into ice.  This occurs because
                    hydrogen bonding pulls the molecule into an open crytalline structure that occupies more space than the liquid.

IV.  Distinguishing Properties of Solids
       A.  Solids have definite volume and definite shape.
       B. Particles have little movement, but they do vibrate against one another.
       C.  Pure solids melt at definite temperatures.
       D.  When solids melt, a definte amount of heat is absorbed.
       E.  Melting Point:  temperature at which a solid turns into a liquid.
            *** The purity of a substance can be determined by the sharpness and temperature of its meltin point.
       F.  Heat (Enthalpy) of Fusion:  total heat or energy required to melt a substance.
       G.  All solids are made of crystals.  Crystals have repeating, 3-D patterns.
       H.  Solids can form allotropes.  Allotropes are two or more different molecular forms of the same element.
             Example:  Allotropes of Carbon
                             Diamond:  each carbon atom is covalently bonding to 4 other carbon atoms to form a network covalent compound.
                                                This is extremely strong.

                            Graphite:  (pencil lead)  - carbon atoms are linked together like a hexagon in layers.  These layers can slide over one another.
                                                                        (very soft)  Each time you write with your pencil a layer slides off onto your paper.

                            Buckyballs (short for Buckminsterfullerene) - most recently discovered allotrope of carbon.  It has 60 carbons
                                                                                                            arranged in pentagons and hexagons.  These form a hollow cage
                                                                                                             which resembles the dome at EPCOT.
        I.  Amorphous Solids:  solids which lack crystals.  They are not true solids.
                                                examples:  plastic, rubber, asphalt, wax, glass.
        J.  Sublimation:  ability to pass from the solid phase to the gas phase without going through the liquid phase.
                                     Examples:    Solid CO2  (dry ice)
                                                           Iodine Crystals
                                                           Camphor (used in air fresheners and moth balls)

V.  Phase diagrams
    -- shows the relationship among solid, liquid, and gas phases in a graph form.

        Tm -  normal melting point            Tb -  normal boiling point
        AB - solid-vapor line                      BC - solid-liquid line
        BD - liquid-vapor line

        triple point:  describes when all three states of matter can exist at equilibrium (at the same time)

        Phase diagrams are different for every type of substance.

VI.  Freezing and Boiling Point Graphs

As you move up the graph from a to e                        As you move down the graph from e to a
a - solid is being warmed                                                e - vapor is cooled
b - solid is melting                                                           d - condensation of vapor
c - liquid is being warmed                                               c - liquid is cooled
d - liquid is vaporized                                                      b - liquid is freezing
e - vapor is being warmed                                               a - solid is frozen

VII.  The 4th State of Matter -- Plasma
        A.  Plasma:  gaseous mixture of electrons and positive ions.
        B.  It behaves as a gas because it has no definite shape or volume.  However, gases are not made up of electrons and positive ions.
        C.  In order for plasma to exist, temperature must be between 50,000 K -  100, 000, 000 K !!!
        D.  True Plasma is found in:
              1.  stars
              2.  the sun
              3.  Van Allen radiation belts that surround earth
        E.  Partial Plasma (plasma that can exist on earth) is found in:
             1.  fluorescent lights
             2.  neon signs
             3.  lightning bolts
             4.  flames

        F.  Aurora Borealis:  also known as the "Northern Lights" is caused by partial plasma in our atmosphere.