Chapter 9

The States of Matter

Kinetic Theory

• Kinetic Energy – 1. energy of motion, 2. particles are in motion, 3. energy the substance has because of it’s motion.

• Kinetic Theory – the tiny particles in all forms of matter are in constant motion.

Three major points

• 1. All matter is made up of tiny particles, which are always moving.

• 2. The higher the temperature, the faster the particles move.

• 3. At a given temperature, lighter particles move faster than heavier ones.

The States of Matter

• The state a substance is in depends on how the particles, which make it up, are moving.

• Solids (s) fixed shape and volume• Liquids (l) fixed volume, takes shape of its

container• Gas (g) no fixed shape or volume• Plasma – very high energy gases in which some or all of

the electrons are removed from the atoms or molecules. (In chemistry we tend to ignore plasmas, leaving them to the realm of the physicists,)

Using this theory as a model, we can explain many things. Let us consider how the particles are arranged in the 3 states of matter. (phases)

Particles have slightly more energy so are able tomove randomly around each other and are spaced slightly further than in a solid. However they do not have sufficient energy to overcome the attractive forces between them so cannot from each other escape completely.

Particles arranged in a regular, close-packed fashion. They have little energy, so simply vibrate about fixed positions, unable to overcome the attractive forces between them.

LiquidSolid Gas

Particles have much more energy so have overcome all attractive forces between them. They move around very fast in a random fashion, colliding occasionally. They are much more spread out then in the solid or liquid state

Gases

1. A gas is composed of particles, usually molecules or atoms.

a. Between the particles is empty space.

b. No attractive or repulsive forces exist between particles.

c. Uncontained gases diffuse into space without limit.

Gases cont.2. The particles in a gas move rapidly in constant

random motion.

3. All collisions are perfectly elastic. “Kinetic energy is completely transferred from one particle to another.” No absorption of the energy by containers, etc.

Gas Dependencies

• Gas Pressure – result of simultaneous collisions of billions upon billions of gas particles with an object.

• Increase or decrease in pressure is indirectly proportional to the space between the molecules or atoms. ( decreasing space, increases pressure)

Gas Numbers to Know

• SI unit for pressure – Pa – Pascal

• Atmospheric Pressure at Sea level = 101.32kPa

• One standard Atmosphere (1atm) = the pressure required to support 760mm of mercury at 25oC.

• STP – standard temperature and pressure = 0oC and 1atm or 101.32kPa or 760mm/Hg

Liquids• Particles in motion, free to slide past one another.

Gases & Liquids flow and are considered to be fluids.

• Intermolecular forces are greater than that of gases and the particles spin and vibrate in fixed positions while moving from place to place.

Solids

•Vibrate around a fixed position•Particles are tightly packed in highly organized patterns.•Denser than liquids and gases and can not be compressed.

State Changes or Phase Change

• When a substance changes state, it is undergoing a physical change, there is no new substance formed. Physical changes unlike chemical changes are easy to reverse.

• Energy is required to turn from solids to liquids, and liquids to gases. In order to gain greater freedom of movement, the forces between the particles must be overcome.

• Energy is given up as gases turn to liquids, and liquids to solids. They move less freely and are held together more strongly.

State or Phase Change Terminology• Evaporation (vaporization) – conversion of a

liquid to a gas or vapor below its boiling point

• Condensation – conversion of a gas to a liquid

• Melting – conversion of a solid to a liquid

• Freezing – conversion of a liquid to a solid

• Sublimation – conversion of a solid directly to a gas with no liquid formation.

• Deposition – conversion of a gas directly to a solid with no liquid formation. (formation of frost)

Changes of State

freezing

Increasing Energy

Gases

Liquids

Solids

boiling condensing

melting

subliming

Temperature Change Terminology• The following are considered to be the

temperature at which the state or phase change occurs at:

• Melting point (mp) - Freezing point (fp)• Boiling point (bp) – condensing point• What is boiling?• Temperature at which the vapor pressure of the

liquid equals the external pressure Boiling temperature changes with external pressure

changes. (e.g. sea level 1000C, atop Mt. Everest 700C for water)