TERM: 2nd TERM
SUBJECT: BASIC SCIENCE
CLASS: JSS 2
WEEK SIX DATE: ………………..
TOPIC: KINETIC THEORY
Kinetic theory of gases - states that gases consist of small particles in random motion. The kinetic particle THEORY explains the properties of the different states of matter. The particles in solids, liquids and gases have different amounts of energy. They are arranged differently and move in different ways.
Property of solids
Property of liquids
Gases are made up of molecules. What are molecules? Molecules are the smallest unit which behaves same as the sample, i.e. they have the same chemical properties as of the sample.
Property of gases
Changes of state
Melting and freezing
If energy is supplied by heating a solid, the heat energy causes stronger vibrations until the particles eventually have enough energy to break away from the solid arrangement to form a liquid.
When a liquid freezes, the reverse happens. At some temperature, the motion of the particles is slow enough for the forces of attraction to be able to hold the particles as a solid. As the new bonds are formed, heat energy is evolved.
Boiling and condensing
If more heat energy is supplied, the particles eventually move fast enough to break all the attractions between them, and the liquid boils. The heat energy required to convert one mole of liquid into a gas at its boiling point is called the enthalpy of vaporisation.
If the gas is cooled, at some temperature the gas particles will slow down enough for the attractions to become effective enough to condense it back into a liquid. Again, as those forces are re-established, heat energy is released.
The evaporation of a liquid
The average energy of the particles in a liquid is governed by the temperature. The higher the temperature, the higher the average energy. But within that average, some particles have energies higher than the average, and others have energies lower than the average. Some of the more energetic particles on the surface of the liquid can be moving fast enough to escape from the attractive forces holding the liquid together. They evaporate.
Solids can also lose particles from their surface to form a vapour. Sublimation is the direct change from solid to vapour (or vice versa) without going through the liquid stage. For example, naphthalene, dry ice of carbon(iv)oxide, Iodine crystals e.t.c
Assumptions of kinetic THEORY of gases:
Precious seed BASIC SCIENCE FOR JUNIOR SECONDARY SCHOOLS BOOK 2 PAGE 134-135.
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