STATES OF MATTER
A. Kinetic Theory
1. Kinetic Energy -- energy of object due to motion
2. Kinetic Theory -- all tiny particles in am object are in constant motion
3. Three assumptions of the theory
a. A gas is composed of particles (molecules or atoms)
b. Gas particles move rapidly in constant random motion
1. Travel in straight paths independently
2. Take shape & volume of container
3. Change direction only when they collide with other molecule or wall of container
c. All collisions are perfectly elastic = energy is transferred without any loss (overall KE stays constant)
B. Gas Pressure
1. The force exerted by a gas per unit surface area of an object
a. Vacuum -- empty space (no particles, no pressure)
2. Atmospheric pressure -- air pressure on earth due to pull of gravity on air molecules
a. Barometer -- instrument used to measure air pressure
3. SI unit of pressure = Pascal (Pa)
a. Atmospheric pressure at sea level = 101.3 kPa = 1 atm = 760 mmHg =
760 torr = 14.7 psi
b. Old units are mmHg and atm which were based on the mercury barometer
c. This value is used for STP calculations
C. Kinetic Energy and Kelvin Temperature
1. What happens when you heat a substance?
a. Some energy is absorbed (potential energy)
b. Some energy makes particles move faster (KE)
1. Faster particles = increase in temperature
2. Each particle doesn't have the same amount of energy
a. Average Kinetic Energy (ave. KE)
3. Temperature = measure of ave. KE
2. Particles would stop moving at some very low temperature
a. No motion, no kinetic energy
b. Absolute zero (0 K, -273 degrees D)
c. Kelvin scale reflects relationship between KE and temperature
1. At a given temperature, ave. KE is always the same
II. The Nature of Liquids
A. A Model for Liquids
1. Liquids flow like gases, but the particles are attracted to each other
a. Intermolecular forces (IM) -- attractive forces between molecules
b. Liquids are denser than gases
1. Increase pressure = no major effect on liquid
c. KE has to be greater than IM forces for molecules to become a gas
B. Evaporation
1. Vaporization -- changing a liquid to gas (vapor) [usually involves adding heat]
2. Evaporation -- change occurs on the surface without boiling
a. Increase evaporation by heating
b. Really is a cooling process (sweating)
1. Particles with highest KE are released, Particles with lowest KE are left behind (hot particles leave, cold particles stay)
3. Closed container is different
a. Particles in liquid vaporize
b. Vapor particles collide with container wall above the liquid -- vapor pressure
c. some vapor particles condense back to a liquid
Liquid <------------ -------- --> Vapor
condensation evaporation
d. Eventually, condensation will equal evaporation -- equilibrium
1. rate of condensation = rate of evaporation
2. Sill condensing and evaporating
4. Increase temperature on closed container, increase vapor pressure
5. Manometer -- instrument used to measure vapor pressure
C. Boiling Point
1. Temperature at which the vapor pressure = external pressure
2. Increae heat, increae KE, increase temperature
a. Reach temperature at which most molecules can evaporate
b. Bubbles of vapor form, rise to surface, & escape
3. Increase external pressure, boiling point increases
4. Decreae external pressure, boiling point decreases
5. Boiling is a cooling process, like evaporation
a. Liquid will never go above boiling point
b. Liquids will just boil faster with more heat added
III. The Nature of Solids
A. A Model for Solids
1. Particles vibrate in fixed positons
2. Packed together in organized patterns
3. Dense and incompressible
4. Do not flow
5. Heat a solid, particles vibrate faster and structure breaks down
a. Melting -- changing from a solid to a liquid
b. Melting point -- temperature at which melting occurs
c. Can do opposite (freeze) at same temperature
solid <-------- --------> liquid
freezing melting
B. Crystal Structure and Unit Cells
1. Crystal -- atoms, ions, or molecules are arranged in an orderly, repeating, 3-D pattern called crystal lattice
a. Regular shapes
b. Shape reflects arrangement
c. type of bonding determines melting point
d. Unit cell -- smallest group of particles within the crystal that retains the geometric shape of the crystal
e. Seven groups of crystals
1. Cubic
2. Tetragonal
3. Orthorhombic
4. Monoclinic
5. Triclinic
6. Hexagonal
7. Rhombohedral
2. Some solids can be in more than one form
a. Allotropes -- two or more different molecular forms of the same element in the same physical state
Example: Carbon = diamond, graphite, or buckyball
3. Amorphous solids
a. Solids with no order structure (not crystals)
Examples: Rubber, asphalt, glass
IV. Changes of State
A. Phase Diagram
1. Gives the conditions of temperture and pressure at which a substance exists as solid, liquid, or gas
2. Each region is a separte phase
3. Curved lines that separate regions represent equilibrium between the two phases based on temperature and pressure (Phase changes)
4. Triple Point -- point at which all three curves meet
a. All three phases are in equilibrium with each other
b. Water = 0.016 degrees C and 0.61 kPa
5. Use diagram to determine changes to melting/boiling points
a. Decrease pressure, melting point increases, boiling point decreases
B. Sublimation -- changing from solid to gas without becoming a liquid
1. Uses -- freez-dried food, dry ice, solid air fresherers, mothballs
Outline based upon:
Matta, M. S., Staley, D. D., Waterman, E. L., & Wilbraham, A. C. (2000). Chemistry, Addison-Wesley. (5th ed.). Menlo Park, CA: Prentice Hall, pp. 267-286.
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