CHAPTER 13 Kinetic Molecular Theory (K.M.T.)

Kinetic Theory: Kinetic Theory: –The tiny particles in all forms of matter are in constant motion. constant motion. –Explains the properties of solids, liquids, & gases.

SOLIDS 1. Solids and K.M.T.  More closely packed than liquids or gases.  Intermolecular forces are VERY effective.  Only vibrational movement.  Crystalline vs. Amorphous (glass) solids.

Properties of Solids 1.Definite shape and volume 2.Melting point:  Crystalline Solids: Definite melting point, KE of particles overcome attractive forces of solid.  Amorphous Solids: No definite melting point, Supercooled liquids. 3. High Density and Incompressibility 4. Low diffusion rate: very slow

Crystalline Solids 1. Crystal structure = 3D arrangement of particles of crystals. 2. Unit Cell = smallest portion of a crystal that shows the 3D structure.

1. no definite shape or volume 2. Particles are small, hard spheres, with insignificant volume (very far apart). insignificant volume (very far apart). 3. Particles move rapidly in constant random motion random motion 4. All collisions are perfectly elastic (Energy is transferred & not lost) (Energy is transferred & not lost) 5. There are no forces of attraction or repulsion between gas particles. between gas particles. Gas Pressure: is the result of simultaneous collisions of billions of gas Gas Pressure: is the result of simultaneous collisions of billions of gas particles with an object. particles with an object.GASES

Gas Pressure: Gas Pressure: is the result of simultaneous collisions of billions of gas particles with an object. is the result of simultaneous collisions of billions of gas particles with an object. Vacuum: when no gas particles are present Vacuum: when no gas particles are present Atmospheric Pressure: results from the collisions of air molecules with objects. Decreases as you climb a mountain b/c air layer around earth thins out at high elevations. Atmospheric Pressure: results from the collisions of air molecules with objects. Decreases as you climb a mountain b/c air layer around earth thins out at high elevations.

Barometer: measures atmospheric pressure Barometer: measures atmospheric pressure –SI unit of pressure = pascal (Pa) –Atm pressure at sea level = STP (0 o C) = kPa = 760 mm Hg= 1 atm= 760 torr= inHg = 14.7 psi Ex: 1.50 atm = ? kPa 1.50 atm kPa = 1.52 x 10 2 kPa 1 atm 1 atm

UNITS OF PRESSURE UnitsSymbolDefinition Millimeters of mercury mmHg Pressure of that supports 1mm of Hg in a barometer Torricellitorr 1 torr = 1 mmHg Atmosphereatm Average atmospheric pressure at sea level at 0°C PascalPa SI Unit for Pressure 1 Pa = 1N/m 2

Barometers

LIQUIDS: Why are they the least common state of matter? 1. Liquids and K.M.T.  Are particles in constant motion? Spacing? Kinetic Energy? Attractive forces? Kinetic Energy? Attractive forces?  Fluid: a substance that flows and hence takes the shape of its container.

Properties of Liquids 1. High Density: 1000x greater than gases, 10% less dense than solids. 2. Relatively Incompressible: Water’s volume only decreases 4% under 1000atm of pressure! 3. Can diffuse: Slower in liquids than gases due to: Slower in liquids than gases due to: slower motion and attractive forces.

Atmospheric Pressure & Boiling Point

Evaporation (vaporization): conversion of a liquid to a gas or vapor below its boiling point. Evaporation (vaporization): conversion of a liquid to a gas or vapor below its boiling point. Vapor Pressure: particles collide with the walls of the sealed container. Vapor Pressure: particles collide with the walls of the sealed container. –Dynamic Equilibrium Boiling Point: temp. at which the v.p. of the liquid is just equal to the external pressure. Boiling Point: temp. at which the v.p. of the liquid is just equal to the external pressure.

Evaporation vs. Boiling

Phase Change Diagrams You will see a heat curve for water in the next slide.

FREEZING, SOLIDIFICATION, CRYSTALLIZATION MELTING CONDENSATION EVAPORATION, VAPORIZATION DEPOSITION SUBLIMATION HEAT OF FUSION 80 cal/g HEAT OF VAPORIZATION 540 cal/g Solid Liquid Gas

FREEZING, SOLIDIFICATION, CRYSTALLIZATION MELTING CONDENSATION EVAPORATION, VAPORIZATION DEPOSITION SUBLIMATION HEAT OF FUSION 80 cal/g HEAT OF VAPORIZATION 540 cal/g Solid Liquid Gas