Kinetic molecular theory and liquids and solids

KMT of Liquids Particles in constant motion, Particles not bound together in fixed position Particles closer together so forces of attraction are more effective, therefore liquids are more ordered than gases Fluidity – “can flow and take shape of container”

Characteristics of liquids High density compared to gases Incompressible, can only decrease volume by 4% at most Ability to diffuse, the higher the temp (KE) the faster to diffuse

Characteristics of liquids Surface tension – The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension Capillary action – attraction of surface of liquid to surface of solid

Vaporization - Phase change examples of VAPORIZATION Evaporation – when particles escape from the surface of a non-boiling liquid and enter the gas state Boiling – conversion of liquid to a vapor within the liquid as well as the surface

EVAPORATION ACCORDING TO KMT Particle with higher than average kinetic energy – at the surface of the liquid – move faster These particles can overcome the intermolecular forces that bind them to the liquid They ‘escape’ into the gas phase Application: How is evaporation a crucial process in nature?

If enough Kinetic energy is removed from a substance Attractive forces pull particles into orderly arrangement Substance becomes a solid Freezing (solidification)

KMT of solids Closely packed Attractive forces hold particles in fixed positions with only vibrational movement around fixed points 2 types of solids Crystalline – orderly geometric repeating pattern Amorphous – randomly arranged particles

Characteristics of solids Definite shape & volume Definite melting point High density Not compressible Low rate of diffusion – almost none

phase A phase - part of a system that has uniform composition and properties. (liquid, solid, gas) Phase change = mixture of 2 phases at same time

Equilibrium What does the word equilibrium mean? A dynamic condition 2 opposing changes occur at equal rates in a closed system.

Pressure Caused by the collisions of molecules with the walls of a container. Gas molecules exert a pressure on any surface with which they collide Depends on temperature, volume and number of molecules

Volatile liquids – evaporate readily , weak forces of attraction between particles Nonvolatile liquids – don’t evaporate readily, relatively strong attractive forces

Equilibrium vapor pressure  

Pressure exerted by a vapor (gas) over its liquid Vapor Pressure Pressure exerted by a vapor (gas) over its liquid

Equilibrium Vapor Pressure Pressure - caused by the collisions of particles with the walls of the container Equilibrium vapor pressure measured when there is equilibrium between gas and liquid phase. rate of condensation = rate of vaporization Number of particles going into vapor phase = number of particles continuing to go into liquid phase