Chapter 16 Section 1Kinetic Theory

Kinetic Theory An explanation of the behavior of molecules

in matter 3 basic assumptions

1. All matter is composed of small particles (atoms, molecules, and ions)

2. These particles are in constant, random motion

3. These particles are colliding with each other and the walls of their container

Thermal EnergyThe total energy of a material’s particles

Kinetic energy + potential energy

AVERAGE KINETIC ENERGY=TEMPERATUREFaster moving particles = higher temp.Slower moving particles =lower temp.Absolute zero = -273.15 C (particle motion is

so slow that no additional thermal energy can be removed)

Solid StateHas a definite shape

and volume

Particles are closely packed together and vibrating in place

Particles have a geometric arrangement

Liquid StateHas a definite

volume, but no definite shape

Particles slip out of their ordered arrangement and are able to move past each other

Still some attractive forces

Liquid StateMelting point – The temp. at which a solid

begins to liquifyHeat of fusion – The amount of energy

required to change a substance from the solid phase to the liquid phase at its melting point

Gas StateNo definite shape or

volume

Particles have enough kinetic energy to overcome the attractive forces between them

Particles bounce and collide, filling their container

Gas StateBoiling point – the temperature at which

the pressure of the vapor in the liquid is equal to the external pressure acting on the surface of the liquid

Heat of vaporization – the amount of energy required for the liquid at its boiling point to become a gas

Gas StateEvaporation BoilingOccurs at the surface of

a liquid

Can occur at temperatures below the boiling point

Must have enough kinetic energy to escape the attractive forces of the liquid

Occurs throughout a liquid

Occurs at a specific temp.

DiffusionSpreading of particles throughout a given

volume until they are uniformly distributedOccurs in solids and liquids, but most rapidly

in gasesFrom high concentration to low

concentration

Heating CurvesShows temp. change as

thermal energy (heat) is added

Temp. remains constant during melting and while boiling

All energy is used to overcome attractive forces

Thermal ExpansionAn increase in the size of a substance when

the temp. is increasedSolids (gaps in sidewalks)Liquids (thermometers)Gases (hot air balloons)

The Strange Behavior of WaterWater molecules have highly positive and

negative areasAs they cool, molecules align themselves by

charge, so empty spaces occur in the structureWater expands as it goes from liquid to solid Ice is less dense than water (that’s why it

floats!)

Plasma StateMatter consisting of

positively and negatively charged particles (neural charge overall)

Very high energy hard collisions of molecules electrons stripped off

Ex - stars, lightning bolts, neon tubes, etc.

Amorphous SolidsNot all solids have a definite melting pointSome merely soften and turn into liquid over

a range of temps.They lack the ordered structures of crystalsEx - glass and plastic (long, chainlike

molecules)

Liquid CrystalsStart to flow during the melting phase similar to a

liquid, but they do not lose their ordered arrangement completely

Highly responsive to temperature change and electric fields

Ex - LCD displays of watches, clocks, and calculators

Changes in Thermal Energy Experiment1. Create a time/temperature table2. Fill your beaker halfway with ice and cold water3. Use your thermometer to measure the

temperature of the water (DO NOT TOUCH THE THERMOMETER TO THE SIDES OR BOTTOM OF THE BEAKER) Record this temp. as time zero

4. Place your beaker on a hot plate over medium heat

5. Measure the temperature every minute and record it in your table

6. Create a graph using your data.7. Write a paragraph describing what is happening

in your graph.