Kinetic Theory

States of Matter

•Liquid•Solid•gas

How are these states of matter alike and different?

Kinetic Theory• An explanation of how

particles of matter behave

3 assumptions of Kinetic Theory

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

2. The particles are in constant, random, motion

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

Thermal Energy

• Total energy of a material’s particles including:–Kinetic energy: vibrations and

movements between the particles–Potential energy: resulting from

forces that act within the particles

Temperature

A term commonly used to describe how hot or cold an object is

However, in science Temperature means the average kinetic energy of particles in the substance

Average Kinetic Energy

How fast the particles in a substance are moving

• Molecules of frozen water at 0°C move much slower than molecules of water at 100°C.

• Molecules have a kinetic energy at ALL temps,

including absolute zero, -273.15°C

• At the temp, though, particle motion is so slow than no more thermal energy can be removed

Solid State

• Particles are tightly packed in a specific ordered geometric arrangement• Particles are strongly attracted to

one another• Molecules are still moving – vibrating

in place

Liquid State

• Particles move faster than those in a solid• This extra energy allows for them to

partially overcome their attractive forces• They have enough energy to break

away from their ordered arrangement in a solid

Particles can slide past one another, allowing for liquids to flow and take

the shape of their container

Since particles do not have enough energy to completely

overcome their attractive forces they cling together,

giving a definite volume

Melting point

• Temperature at which a solid begins to liquefy• As particles are heated they move faster• They bump into one another and transfer

their energy to adjacent molecules• When particles of a solid gain enough kinetic

energy to slip out of their ordered arrangement the solid melts

Heat of Fusion

• The amount of energy needed to change a substance from the solid to the liquid phase.

Gases

Particles have enough kinetic energy to completely overcome

the attractive forces between them

Gases do not have a fixed volume or shape

Vaporization

• When liquid particles are moving fast enough to overcome their attractive forces and enter the gas state– There are two modes of vaporization

1. Evaporation2. boiling

Evaporation

• Can occur at a temp below the boiling point• Only occurs on the surface of a liquid• Particles have enough energy to break away

from the liquid

Boiling

• Occurs at a specific temp • Also depends on the pressure on the liquids

surface• Occurs throughout the liquid

• There is an external pressure (air) pushing down on the surface of the liquid

• The force of this pressure keeps the liquid particles from escaping

• Boiling Point: the temp when the pressure of the vapor in the liquid is equal to the external pressure

• Gas particles move about randomly• The movement of gas particles and the

collisions between them cause gases to diffuse

Diffusion

Spreading of gas particles throughout a given volume until

they are equally distributed

Heating curve of a liquid

• All particles of water at -20 ° are in the solid state

• If heat is applied, the temp increases to 0° where the ice begins to melt

• Once the ice begins to melt the temp stays constant until ALL ice is melted.

• All energy is put into overcoming the attractive forces in the solid

Once the ice is ALL melted, the particles are all moving freely and their avg kinetic energy begins to

increase

• When the temp reaches 100°C the liquid begins to boil

• The temp will remain constant until ALL of the liquid’s particles have overcome their attractive forces

Plasma

• Matter consisting of positively and negatively charged particles

• Overall charge is neutral due to equal number of each

• Particles are moving SO fast that when they collide they strip atoms of electrons

• Most common state of matter in the universe

• Also found in lightening blots, neon and fluorescent tubes and auroras

Thermal Expansion

• When heated particles move faster• As they speed up they move farther apart• Also, when cooled, particles slow down and

the attractive forces are stronger causing the particles to come closer together – shrinking of an object

Expansion in Liquid

• Thermometers: the liquid inside expands when heated

• This causes it to fill more of the narrow tube

Expansion in gases

• Hot air balloons: the particles of heated air inside the balloon move faster and spread apart

• This makes the density of the air in the balloon less than the density of the cooler air outside of the balloon

• The balloon then rises

Water

• Water works oppositely: it expands when cooled and shrinks when heated

• Water is a polar molecule (means it has positive and negative poles)

• These charged regions affect the behavior of water

• When the water cools and the molecules slow down they become more attractive and move closer

• Because of the positive and negative charges they can only arrange themselves in a specific manner

• Pos and neg charges will line• This results in spaces or gaps

• The empty spaces are larger in solid ice than liquid water

• This results in a lesser density and why ice floats

Density of Different forms of Water

Amorphous solids

• No exact temp where phase change occurs (boiling point)

• Soften and gradually turn into a liquid over a temp range

• Due to irregular particle arrangement. Jumbled chains and not neat geometric arrangements

Amorphous solids

Liquid crystals

Normally the ordered geometric structure of a solid is lost when it becomes a liquid and gas

Liquid crystals begin flowing like a liquid when they melt BUT they keep their geometric order

Liquid Crystals