IV. Answer the following questions:

1. A bag of cement lying in the open gets wet due to rain during the night. The next day the

sun shines brightly. Do you think the changes, which have occurred in the cement could be

reversed? Explain.

(2, A potter working on his wheel shaped a lump of clay into a pot. He then baked the pot in

an oven. Do these two acts lead to the same kind of changes? Justify your answer.

3) Give three applications of heating and cooling in materials.

4) Plastic do not conduct heat as well as iron. Give reason

1-Turning Portland cement into concrete is a one way reaction. The reaction takes place because of water. You cannot reverse it ... So, without another chemical reaction, it will never be made liquid.

2-No, before it is baked it isn't hardened yet therefore doesn't have the same texture.

3-air conditioning, space heating, power generation, and chemical processing.

4-Plastic is a poor conductor of heat and also of electricity. Normally a substance which is a good conductor of electricity is also a good conductor of heat as well, a substance which is a poor conductor of electricity is also a poor conductor of heat. One substance which is a poor conductor of electricity but a good conductor of heat is mica. The electric heating element used in irons (used for ironing of clothes) is enclosed in flakes of mica and mounted on the iron's base above it is a layer of asbestos and a heavy flat iron in the shape of the iron base (to keep the heating element and asbestos sheet pressed). Mica conducts the heat to the iron base but not the electricity.