Kinetic molecular theory and liquids and solids

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”

KMT 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

Characteristics of liquids

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 phaseApplication:How is evaporation a crucial process in nature?

If enough Kinetic energy is removed from a substanceAttractive forces pull particles into orderly arrangement

Substance becomes a solid

Freezing (solidification)

Closely packedAttractive 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

KMT of solids

Definite shape & volumeDefinite melting pointHigh densityNot compressibleLow rate of diffusion – almost none

Characteristics of solids

phaseA 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

 

 

Vapor Pressure

Pressure exerted by a vapor (gas) over its liquid

Equilibrium Vapor PressurePressure - 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