States of Matter

The Kinetic-Molecular Theory of Matter

The kinetic molecular theory of matter whas devolped in the late nineteenth century, to account for the behavior of the atoms and molecules that make up matter.
The offical definition of the Kinetic-molecular theory is- the idea that particles of mattter are always in motion. The thery is used primarly to explain properties of solids, liquids,gases in terms of energy and the forces that act between them.

The Kinetic-Molecular Theory of Gases

*Ideal Gas – hypothetical gas that perfectly fits all the assumptions of the kinetic molecular theory

The kinetic Molecular Theory of Gases is based on five assumptions.
  1. Gases have many particles that are far apart relative to their size. Most of the volumes of gasses is empty space. Lastly the gas has a lower density (easily compressed).
  2. That when their are collisions between gas particles and between particles and container walls and there is no net loss of toal kinetic enerfy (an elastic collision). Also kinetic energy is transferred during collisions.
  3. THe gas particles are in continuous, random, rapid motion, which equals kinetic energy. Also the kinetic energy of particles overcomes attractive forces between them, EXCEPT when teh temperature is where gas becomes liquid.
  4. There is no forces of attraction between gas particles
  5. The temperature of a gas depends on the average kinetic energy.

  • *Kinetic Energy Calculation – * m-mass v-speed
    Speed - increase = high temp decrease = low temp
The Kinetic-Molecular Theory and the Nature of Gases
  • Gas expands to the size and shape of it’s container
  • Gas particles glide easily past each other like water (both considered fluids)
  • Gas has a low density (about 1/1000 of the same substance in liquid or solid form)
  • The volume of a gas can be greatly decreased (compressed)
  • Gases will spread and mix with each other without being stirred
*Diffusion – spontaneous mixing of the particles of two substances caused by their random motion
*Effusion – a process by which particles pass through a tiny opening

  • The rate of effusion is proportional to the velocity of the gas particles
Deviations of Real Gases from Ideal Behavior
*Real Gas – a gas that does not behave completely according to the assumptions of the kinetic-molecular theory

  • The kinetic-molecular theory is most likely to hold true to noble gasses
    • examples are helium.He and neon Ne, are what ideal gas behavior is over temperatures and pressures.


  • Liquids are the least common state of matter in the universe
  • Liquids have a definite volume and take the shape of it’s container
  • Liquid molecules are closer together and are attracted to each other
*Fluid – a substance that can flow and therefore take the shape of its container

  • Most liquids flow downhill due to gravity
- Liquid helium near absolute zero can flow uphill

  • Liquids have a higher density to the close arrangement of particles
  • Water is one of the few substances the becomes less dense when it solidifies
  • Liquids are much less compressible that gases
- Liquids can transmit pressure equally in all directions (like gas)

  • Liquids diffuse at a slower rate then gases (speed depends on temperature)
*Surface Tension – a force that tends to pull adjacent parts of a liquid’s surface together, thereby decreasing surface area to the smallest size possible (applies to all liquids)

  • The higher the force of attraction, the higher surface tension
  • Water has a higher surface tension than most liquids
- Hydrogen bonds in water cause them to attract more
*Capillary Action – the attraction of the surface of a liquid to the surface of a solid

  • Capillary action is closely related to surface tension
- A liquid will rise quite high in a narrow tube
- The attraction between liquid molecules and the molecules that make up the surface of the tube tends to pull the liquid molecules upward along the surface of the tube against the pull of gravity
*Vaporization – the process by which a liquid of solid changes to a gas
*Evaporation – the process by which particles escape from the surface of a nonboiling liquid and enter the gas state (a form of vaporization)

  • Evaporation occurs because the particles of liquids have different kinetic energies
- Some surface particles with higher-than-average energies can overcome the intermolecular forces that binds them to the liquid
*Boiling – the change of al liquid to bubbles of vapor that appear throughout the liquid
*Freezing (Solidification) – the physical change of a liquid to a solid by removal of energy as heat

Kinetic molecular theory (KMT)- explains the behavior of moving particles
-gases that obey the KMT are called ideal gases
-gases that almost obey KMT are real gases
-the energy of a particle can be determined by using KE= 1/2mv^2
*the state of a substance depends on a battle between kinetic energy and it's inter-molecular attractive forces*
3 Types of Inter-Molecular Forces (weakest to strongest)
1) London Dispersion Forces - (always present) comes as a result of the random movement of electrons instantaneous (temporary) partial charge
- stronger and larger molecules (more electrons)
EXAMPLE: CH4 (5 atoms) vs C8H18 (26 atoms)
weaker dispersion stronger dispersion
lower boiling point higher boiling point
2) Dipole- dipole
found only in polar molecules (HCl)
3) Hydrogen Bonding
- strongest of the 3 IM forces
- exists in compounds where "H" is directly bonded to "N" "O" or "F"

Pressure - force/area = n/m2 = Pascal (Pa)
KPa = atmospheric (atm) = mmHg = torr = psi
- atmospheric = pressure at sea level
101.3 KPa = 1 amt = 760 mmHg = 760 torr = 14.7 psi
*use stoichometry to convert pressures*
EXAMPLE = Convert 19.2 psi to mmtlg
19.2 psi (760 mmtlg / 14.7 psi) = 993 mmHg
Measuring Pressure
1.) Barameter- measure atmospheric pressure
2.)Manometer-measures has pressure if the atmopheric pressure is 770mmHg what is Has A's pressure?
7708mmHg = 18mmHg
Vapor Pressure- a pressure resulting from the vaporization of a liquid
-volatile lquid- a liquid that exhibits a high vapor pressure
Boiling Point- the temperature at which the vapor pressure of a liquid is equal to the atmospheric pressure

Heating Curves
external image sci_dia_21.gif

Cwater = 4.184 Joules/(grams)(temp Celcius)
Cice = 2.06 Joules/(grams)(temp Celcius)
Csteam = 1.87 Joules/(grams)(temp Celcius)
*use the equation q=mc(delta)T to solve the amount of energy that is need to heat a substance from an ice to a liquid to a gas.
*heat of fusion (crystalization) - the heat required to melt 1 mol of a substance.
  • Hfus = 6.02 kiloJoules/mol

*heat of vaporization - heat required to vaporize 1 mol of a subtance
  • Hvap = 40.7 kiloJoules/mol

external image PhaseDiagram.jpg
solid to gas = sublimation
gas to solid = deposition