STATES OF MATTER And other stuff
Kinetic Molecular Theory • States that particles in all forms of matter are in constant motion. • Three types of motion: vibration, rotation, and translation • Explains the fluidity of gases and liquids and how odors move through the air.
KMT is used to describe states of matter based on the energy and motion of the particles
Gas Model High energy No definite shape or volume Compressible Low density Weak intermolecular forces
Fivebasic assumptions of kinetic theory as it applies to gases: (p 475) • Composed of tiny particles • Particles are so small compared to volume of gas that their volume is considered insignificant/negligible. • Assume attractive or repulsive forces among particles is negligible
continued • Constant random motion with straight paths that change direction after collisions. Avg. Speed 1700km/hr Collisions are elastic – no energy is lost- it is transferred – total KE is constant at constant temperature 5.Avg KE directly proportional to Kelvin temp.
Gas Pressure • Result of collision of particles with each other and walls of container • Force per unit of area • Smaller container with same amount of gas creates more collisions and greater pressure • No gas, no collisions, no pressure =? • vacuum
Atmospheric Pressure • Collisions of air molecules with objects • Barometer – instrument used to measure atmospheric pressure • Mercury and aneroid • SI unit pascal (Pa) @ sea level 101.3 kPa • Also, atmospheres, torrs, mm Hg • Must relate to STP OoC and 101.3 kPa
KE and Kelvin Scale • Increase average KE = increase in temp. • All particles do not have the same KE • Some low, medium, & high – mostly med. • No KE = 0 Kelvin = absolute zero • Kelvin temperature is directly proportional to the average KE of particles EX. He gas at 200K has twice as much KE as particles at 100K
Liquid Model • Definite volume but no definite shape • Attraction among particles (intermolecular forces) • Particles have enough energy to change position • Motion contributes to average KE • To “escape” (become a gas) must absorb enough energy to overcome intermolecular forces
Liquid to Gas • Evaporation vs Vaporization not boiling boiling • Evaporation is actually a cooling process – particles with highest KE escape thereby decreasing temperature • Vapor pressure is created when a liquid is in a sealed container and particles evaporate forming a gas over liquid
Equilibrium reached when the number of particles vaporizing and condensing is the same • Increase temp. will increase vapor pressure (more particles have minimum KE) • Vapor pressure is measured with a manometer
Boiling Points • Temperature at which vapor pressure of a liquid equals the external pressure. • Why boiling point for water changes with elevation • Normal boiling point = BP at 101.3kPa • Boiling like evaporation is a sort of cooling process (for the liquid)
Solid Model • Definite shape • Definite volume • Particles vibrate around a fixed position • Particles are usually tightly packed in organized patterns (crystals) • Amorphous solids lack internal structure (glass, plastic, rubber)
Melting Points • Temperature at which a solid becomes a liquid • Melting and freezing points are the same – just a matter of whether energy is being absorbed or lost • Note: not all solids melt – some decompose
Phase Diagram • Conditions of temperature and pressure at which a substance exists as solid, liquid, and gas.
GASES • Assumes Volume • of Container • Compressible • SOLIDS • Diffuses Rapidly Takes Shape of Container • Definite Shape Definite Volume • Does Not • Flow Flows Readily • Diffuses • Extremely • Slowly Incompressible • Viscosity • Surface Tension • Diffuses Slowly LIQUIDS
Exothermic – heat (energy) released • Endothermic – heat (energy) absorbed • Is boiling endo or exo? • Is melting endo or exo?
Terms you need to know • Volatile – a substance that vaporizes readily (low intermolecular forces) Diffusion – mixing due to molecular motion Viscosity – resistance to flow Surface tension – tendency of a liquid to maintain a minimum surface area (high intermolecular forces)