SELECTED PRINCIPLES: KINETIC THEORY
Diffusion, the movement of particles from a high to low concentration,
and Brownian Motion, the random movement of solid particles suspended
in a liquid or in a gas, are two pieces of evidence which provide the
basis for the kinetic particulate theory of matter - a model which is
used to explain various physical properties of substances.
The main points in the kinetic theory of gases can be summarized as follows. One, a gas consists of particles in ceaseless random motion. Two, the volume of the particles themselves is negligible in comparison with the total volume of the gas. Three, the particles exert neither attractive nor repulsive forces on one another. Four, the particles make elastic collisions; i.e., no energy is lost in collisions between the particles. And five, the average kinetic energy of the particles is proportional to the absolute temperature of the gas.
Strictly speaking, the kinetic theory refers only to gases. However, because the difference between the three states of matter is to do with the amount of energy each state has (i.e., gas > liquid > solid), parts of the theory are used to provide a model of each of these states; the Table below summarizes their characteristic properties.
 
    SOLIDS
   LIQUIDS
   GASES
Kinetic energy of particles
None
Low
High
Motion of particles
Vibrate about
fixed positions
Freely around
one another
Ceaseless
and random
Rate of diffusion
Very slow
Slow
Fast
Attractive forces
Strong
Fairly weak
Negligible
Spacing of particles
Close contact
Close contact
Far apart
Arrangement of particles
Regular
Random
Random
Volume
Fixed
Fixed
Variable
Shape
Fixed
Variable
Variable
Compressibility
Virtually
incompressible
Only slightly
compressible
Very
compressible
Density
High
High
Very low


1.  The average kinetic energy, and so the average speed, of molecules 
in a gas increases with temperature. Although the derivation of any of 
the mathematical equations associated with the kinetic theory of gases 
is beyond the scope of this text, advanced studies do show that the
average speed of gas molecules can be calculated using this equation,
where: R is a constant, with a value of 8.314 J K- mol-; T is the
temperature (in K); and, M is the molar mass (in g mol-).
Complete this Table, using the equation above to calculate the average
speed of the molecules of these gases at 723 K (450C).
 
 Average speed of molecules / m s-
 Gas 
 M / g mol-
 at 298 K
 at 373 K
 at 723 K
 Dihydrogen (H2)
      2
   1928 
   2157 
      
 Methane (CH4)
     16
    682
    763
 
 Ammonia (NH3)
     17
    661
    740
 
 Carbon monoxide (CO)
     28 
    515 
    576 
 
 Dinitrogen (N2)
     28 
    515 
    576 
 
 Ethene (C2H4)
     28 
    515 
    576 
 
 Ethane (C2H6)
     30
    498
    557
 
 Dioxygen (O2)
     32
    482
    539 
 
 Propane (C3H8)
     44
    411 
    460 
 
 Butane (C4H10)
     58 
    358 
    401 
 
 Sulfur dioxide (SO2)
     64
    340 
    381 
 
                                                                    [7]
2.  In everyday-life, water is the substance most commonly observed in
its three physical states (usually known as ice, water, and steam); the 
diagram below shows the processes accompanying the physical changes.
(a) Calculate the heat energy (H) needed to melt one mole of ice at
273 K. [Use the equation  H = m  l, where: m is the mass of substance;
and, l is the specific latent heat of fusion of ice, with a value of
0.334 kJ g-.] ________________________________________________________
(b) Calculate the heat energy (H) needed to increase the temperature of
one mole of water from 273 to 373 K. [Use the equation  H = m  c  DT,
where: m is the mass of substance; c is the specific heat capacity of
water, with a value of 0.00420 kJ g- K-; and, DT is the temperature
rise.] ________________________________________________________________
(c) Calcuate the heat energy (H) needed to vaporize one mole of water
at 373 K to steam. [Use the equation  H = m  l, where: m is the mass
of substance; and, l is the specific latent heat of vaporization of
water, with a value of 2.26 kJ g-.] __________________________________
(d) State the total amount of heat energy released to the surroundings
when one mole of steam at 373 K is converted to ice at 273 K. _________
_______________________________________________________________________
                                                                    [7]
3.  Name the process in which molecules go directly from the solid 
into the vapour phase; as is observed, for example, with carbon dioxide
[solid  gas]. ___________________________________________________
                                                                    [1]
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