Question

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Answer 1

Answer:

1. Physical change is the change in the physical states, shapes and size with any change in chemical compound.

Eg - Cutting of paper

2. Chemical change occur when a substance combines with another to form a new substance, or when the chemical compound of the substance changes.

Eg - Cooking of food

3. Galvanisation is the process of coating zinc on iron to prevent rusting.

4. Crystallisation is defined as a process by which a chemical is converted from a liquid solution into a solid crystalline state.

5. a) Oiling or greasing

b) Galvanisation

Answer 2

Answer:

1. A substance is said to undergo a physical change when only the physical properties such as the shape, size, colour, state or appearance of the substance change. Its chemical composition remains intact. Some Characteristics of a physical change are:

• Temporary in nature.
• Does not affect the internal structure of a substance, only the molecules are rearranged.
• No new substance is formed.
• Most of the physical changes are reversible. We can obtain the substance back even after the change.

Some examples of a physical change are folding of a paper sheet, melting of wax, freezing and boiling water.

2. A substance is said to undergo a chemical change when the chemical properties of a substance alter. As a result, there is either formation or breaking of atomic bonds at the molecular level.

Some characteristics of a chemical change are:

• Permanent in nature.
• Since the original composition of the substance changes, one or more new substances are formed.
• Forms of energy, such as heat, light or electricity, may be emitted or absorbed.
• A chemical change is generally irreversible. At least, it cannot be reversed by simple physical means.

Some examples of a chemical change are burning of paper, burning of fuel, rusting of iron, the souring of milk.

3.Galvanization is the process of applying a protective layer of zinc on a metal. It is a very common method of preventing the rusting of iron. This can be done by dipping the metal to be protected in hot, molten zinc or by the process of electroplating.

The protection of iron and steel from corrosion by coating with molten zinc. has been proved for a hundred and fifty years.

The zinc coating protects from the atmosphere the part’s surface, avoiding corrosion and weathering.

4.Crystallization is a technique used for the purification of substances. A separation technique to separate solids from a solution. Crystallization can be defined as the process through which the atoms/molecules of a substance arrange themselves in a well-defined three-dimensional lattice and consequently, minimize the overall energy of the system. When a substance is subjected to crystallization, its atoms or molecules bind together through well-defined angles.

5. The two preventive measures are as follows:

1. Apply Oil: A coating of oil will help to prevent rust or slow it down, since it inhibits moisture from reaching the iron in the metal. However, an oily surface might be problematic for some tools or machines and poses environmental and human health concerns.
2. Paint the Metal: A good quality paint will slow down rusting by preventing moisture from reaching the metal.