Kinetic Theory Of Matter

CONTENT
• States of matter
• Change of state: melting, boiling, evaporation, condensation and freezing
• Kinetic theory of gases
• Phemomena supporting kinetic theory of matter

STATES OF MATTER

The three states of matter: solid, liquid and gaseous states can be distinguished by the motion of particles they are made of and the attractive force between their particles.

SOLID LIQUID GASES

Have definite shape and volume Have no definite shape but definite volume Have no definite shape and volume
Very dense Less dense Least dense
Incompressible Incompressible Compressible
Fixed mass Fixed mass Fixed mass
Particle vibrate and rotate about a fixed point Particles vibrate and move about within a restricted space Particles move about constantly at great speed and at random

CHANGE OF STATE

MELTING

Melting is the physical process where a substance changes from a solid to a liquid. When a solid is heated, the particles acquire greater kinetic energy and move violently. A point is reached when the forces of vibration overcome the cohesive forces holding the solid particles together and the crystalline structure collapses. The particles are no longer held in fixed positions but are free to move about and the liquid state is reached. The temperature at which this occurs is called the melting point of the solid.

BOILING

When a liquid is heated, the rate of evaporation increases and the value of the saturated vapour pressure equal the prevailing atmospheric pressure. When this happens, the liquid is said to boil and the temperature at which this happen is known as the boiling point of the liquid.
The boiling point of a liquid change with change in atmospheric pressure. If the pressure is raised, the boiling point will increase and if the pressure is lowered the boiling point will decrease. Also, the presence of impurities increases the boiling point of a liquid.

EVAPORATION

Evaporation is the process of vapourization of liquids at all temperatures. When the surface of a liquid is exposed, the molecules near the surface of the liquid will acquire extra kinetic energy, large enough to enable them break away from the cohesive force binding them to the neighbouring particles. Once free, they escape from the liquid surface to become molecules in the vapour state.

Evaporation results in decrease in the volume of liquid and lowering the temperature of the liquid, therefore it causes cooling. Also, it occurs at all temperature but increases with increase in temperature. In addition, it is slower in electrovalent liquids than in covalent liquids.

DIFFERENCES BETWWEEN EVAPORATION AND BOILING

EVAPORATION BOILING

Takes place at the surface of the liquid Involves the entire volume of the liquid
Takes place at all temperature Takes place at a fixed temperature

CONDENSATION AND FREEZING

Condensation is a process whereby a vapour loses some of its kinetic energy to a colder body and changes into the liquid state.
When a liquid cools, it loses heat energy to its surroundings, causing its temperature to drop. If the cooling continues, the temperature of the liquid keeps dropping until it reaches the freezing point of the liquid. At this temperature, the liquid changes into solid.

EVALUATION

1. Describe the melting process of a solid.
2. State two differences between evaporation and boiling.

KINETIC THEORY OF GASES

The theory postulates the following for an ideal or perfect gas:
Gas molecules are in constant, rapid, straight motion, colliding with one another and with the walls of the container.

The collision of gas molecules is perfectly elastic.
The total volume of the gas molecule is negligible compared to the volume of the container.
The force of attraction between the gas molecules is negligible.
The average kinetic energy of the molecule is a measure of the temperature of the gas molecules.

PHENOMENA SUPPORTING THE KINETIC THEORY OF GASES

Brownian motion:

This is the constant, irregular movement of particles in a liquid or gas. It shows that gas molecules are in constant motion.
Diffusion: Diffusion is the movement of particles from a region of higher concentration to lower concentration. Diffusion is common in gases and it results from the random movement of particles of a gas.

GENERAL EVALUATION/REVISION

1. Compare the three states of matter under the following headings: Shape/volume, Density, Compressibility and Motion of particles.
2. Write short note on (a) Boiling (b) Evaporation.
3. 100cm3 each of 0.02moldm-3 solution of HCl and Pb(NO3)2 were mixed. Assuming the PbCl2 is completely insoluble; determine the mass of the PbCl2 precipitated.
4. State the postulates of Dalton’s Atomic theory.

READING ASSIGNMENT
New School Chemistry for Senior Secondary School by O.Y. Ababio, Pg 71-77
WEEKEND ASSIGNMENT

1. —— is measure of the average kinetic energy of the molecules of a gas. A. mass B. volume
   C. pressure D. temperature.
2. All the following are the assumptions of the kinetic theoryof gases except A. Gases are composed of many elastic particles called molecules. B. The molecules are of negligible C. The molecules collide with one another and with the walls of container.D. The molecules are in constant random motion.
3. Presence of sodium chloride in ice will A. decrease the melting point of the ice B. increase the melting point of the ice C. make sodium chloride impure D. lower the freezing point of sodium chloride
4. Which of these does not support the kinetic theory? A. Brownian motion B. Diffusion C.Osmosis
   D. Linear expansivity
5. The phenomenon whereby the atmospheric pressure equals the saturated vapour pressure is called
   A. freezing B. latent heat C. boiling D. normal pressure

THEORY

1. A bottle of milk is taken out of the refrigerator and placed on the table. Droplets of water are noticed on the surface of the milk bottle. Explain the observation
2. State two phenomena that support the kinetic theory of gases.