Kinetic Molecular Theory

Kinetic Molecular Theory

Scientists use a model to develop a theory about the behavior of all states of matter.

Model

• A verbal, mathematical, or visual representation of a scientific structure or process.

• Models are sometimes used as a basis for creating theories.

Ex: A model of the solar system

Theory

• A scientific explanation that has been supported by consistent, repeated experimental results.

• Can be modified if new experimental data arise.

Ex: Theory of gravity that explains the movement of planets

Explaining Properties of the States of Matter

All matter is made up of very small particles

Particles are so small, they cannot be seen even with a microscope.

Particle Model of Matter

Kinetic Molecular Theory…

• All matter is made up of small particles

• The particles exist in empty space and are constantly moving.

• Energy makes particles move.

More Energy = Faster Movement = Move Faster Apart

• Explains the properties of solids, liquids and gases.

Solid

• Very close together

• Vibrate but do not move

• Attract each other strongly in rigid structure.

Liquid

• Very close together

• Slip and slide past and revolve around each other.

• Attract each other lessstrongly than in solids.

Gas

• Very far apart compared to size.

• Move randomly and quickly in lines.

• Attraction to each other is almost zero.

State of Matter Solid Liquid Gas

Movement

Particles vibrating

in place

Particles

sliding past

each other

Particles

freely moving

Shape FixedFits shape of

containerFits shape of

container

Volume Constant ConstantVaries

depending on container

We can use KMT to explain changes of state. But before we do that, we need to note a few things about temperature.

• Temperature is a measure of the average kinetic energy of particles in a substance.

• Adding or removing energy from matter changes the temperature of the matter.

• Increasing temperature of matter means that particles are gaining energy.

*** KMT can be used to explain many other phenomena such as diffusion or thermal expansion!***

Vaporization (Boiling)

• Liquid particles move freely around each other. Particles are still close and attracted to each other.

• As temperature increases, kinetic energy increases.

• Particles move faster. Some gain enough energy to overcome attractive forces and escape into the air.

Freezing (liquid to solid)

• Liquid particles lose kinetic energy as temperature decreases.

• They move slower, attractive forces between particles increase.

• They slow down to the point where they vibrate beside each other.

*** KMT can be used to explain many other phenomena such as diffusion or thermal expansion!***

5b Changes in States of Matter

(not in notes)

States of Matter

• Matter exists in different states

• Solid

• Liquid

• Gas

(and plasma)

Adding Energy to Matter

• As you add energy to a solid, the particles speed up.

• Eventually the particles have enough energy and space between them to slide by each other, and the substance turns into a liquid.

• This is known as MELTING– i.e, ice cubes taken out of the

freezer

Adding Energy to Matter

• If you continue to add energy to the liquid, the particles speed up and move away from each other.

• Eventually they break free of the forces of attraction between the particles, and the substance turns into a gas.

• This is known as VAPORIZATION– I.e., boiling water turning into

steam

• If you quickly add a large amount of energy to a solid, the particles can quickly move from vibrating in place, to moving very quickly.

• The substance can then ‘skip’ the liquid state and turn directly into a gas

• This is known as SUBLIMATION– i.e., ‘fog’ produced from ‘dry

ice’ (frozen carbon dioxide)

Adding Energy to Matter

Removing Energy to Matter

• As you take away energy from a gas, the particles slow down and move closer together.

• Eventually the force of attraction becomes too strong for the particles to move freely, and the gas turns into a liquid.

• This is known as CONDENSATION– I.e., water droplets forming on

the bathroom mirror during a shower

Removing Energy to Matter

• If you continue to remove energy from the liquid, the particles slow down even more.

• The particles eventually become locked in place, only vibrating back and forth, and the substance becomes a solid.

• This is known as either FREEZING or SOLIDIFICATION.– i.e., ice forming on the top of a

pond in winter

• If you quickly remove a large amount of energy from a gas, the particles suddenly slow down and move closer together.

• The substance can completely skip the liquid state and turn directly into a solid.

• This is known as DEPOSITION– i.e., frost forming on the grass

on a cold morning

Removing Energy to Matter

States of Matter and Thermal Expansion

• As particles move faster, they generally spread out and require more space.

• Therefore, under normal circumstances, when you heat up a substance, the particles move away from each other and the substance will expand.

Expansion of Ice and Water

• water is one of the rare exceptions to the expansion rule!

• We know that ice is LESS DENSE than liquid water since ice cubes float to the top of your glass and ice forms on the surface of a lake, not on the bottom!