1. Physical changes: Here no new substance is formed but only physical properties change.

Melting ; it is the process at which a substance change from solid to liquid. E.g. ice melts at 0^oc.

Boiling; it is the process at which a substance changes from liquid to gas. E.g. water boils at 100^oc where atmospheric pressure is 1atm.

Changes of state of matter

• Vaporization ; it is the change of state of matter from liquid to gaseous state, when ice is heated it melts to form water and as heat is supplied continuously, it evaporates to the gas state so vaporization and evaporation is the same.
• Condensation; it is the change of state from gas to liquid state. E.g. change of vapour to water, when air is cooled it turns into a liquid.
• Sublimation; it is the transition of matter from the solid state t o the gas state without passing through the liquid state. E.g. iodine sublimes to be a gas.

Chemical changes

Here new substances are formed. A change of color or odour is a good indication that the substance is changing chemically.

Thermal and electrical insulations

1. Thermal insulation: these are materials that do not allow heat to flow through them since they lack free moving electrons. They are non metals. Generally most liquid and gases are relatively poor thermal conductors hence are good thermal insulators. Gases are very good insulators than liquid because their molecules are close together and collide more often.

Remarks

1. Cooking pot are made of metals so they can easily conduct heat to the food inside the pot.
2. Handles of pots and pans are made plastics to prevent flow to the hands of the owner.

2. Electrical insulator: electrical conductors are simply materials that cannot conduct electricity. They do not allow charge particles (electrons) to flow through them. They include; rubber, plastic, air, and glass.

Uses of electrical insulators

• Used to insulate the circuit and prevent human contact with current in live wire
• Used in portable hand held electrical equipments to prevent harmful shocks

Remarks:

• When insulators are subjected to high voltage, they suffer from electrical break down then they can suddenly become conductors and a large current flow through them.

Heat transfer

Heat energy can be transferred from one place to another. Heat is transferred in 3 main processes;

Conduction, convection and radiation.

1. Conduction: it is the process by which heat energy is transferred between particles as they collide within a material or between two materials in contact.

When a metal rod is heated, the rapid moving air molecules near the flame collide with atom at the end of the rod. The energy transferred to the metal atom causes them to vibrate violently colliding with a slowly vibrating atom transferring energy as heat along the rod. This energy can be transferred to your skin causing a hot sensation.

N.B; conduction takes place in objects in contact and at different temperatures

2) Convection: It is the heat transferred by the movement of fluids with different temperature. When water is heated in a pot the water molecules under the pot becomes hot and expands as a result, the water becomes less dense and moves upwards carrying alone its extra energy. The rising warm air is replaced by cool and dense air from the water top. They are thermally heated in the process. Convection current is setup and the whole water is warmed up

• Convection is used in heating and cooling of the house. Here the warm air from the floor level rise up while the cool air from the ceiling sinks to the floor, an air conditioner makes use of the process

3. Radiation: it is the process of heat transfer by electro-magnetic waves. E.g. u.v. rays, infrared waves, and light. Heat energy from the fire side reaches our leg by radiation. A hot object radiates more energy than the cool one.