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Question

Select the chemical changes from the following:
(i) Digestion of food
(ii) Boiling of water
(iii) Cooking of food
(iv) Tarnishing of silver spoon
(v) Sublimation of iodine
(vi) Electrolysis of water
(vii) Melting of butter in a pan
(viii) Burning of wood


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Solution

  1. Chemical change: The changes in which new substances are formed are called chemical changes.
  2. In a chemical change, one or more kinds of matter are transformed into a new kind of matter.
  3. It is a permanent change and cannot be easily reversed.
  4. Physical changes are those in which the physical properties of the substances change. It is reversible and no new product is formed.

The chemical changes from the following are -

(i) Digestion of food:

  1. It is a chemical change because enzymes that are present in the stomach and intestines break down large macromolecules into simpler molecules so that the body can more easily absorb the food.
  2. Food breakdowns and forms the new substance.

(ii) Cooking of food:

It is a chemical change because after cooking the food, the raw ingredients or the vegetables cannot be regained again.

(iii) Tarnishing of silver spoon:

  1. Tarnishing of the silver spoon is actually the result of a chemical reaction between the silver and sulphur-containing substances in the air.
  2. Silver gets oxidized in the presence of oxygen in the air.

(iv) Sublimation of iodine:

  1. Sublimation of iodine occurs when it is heated.
  2. It is a chemical process because it cannot bring back to solid.

(v) Electrolysis of water:

  1. Electrolysis of water means the breakdown of water into hydrogen gas and oxygen gas.
  2. But when hydrogen and oxygen gas come in contact they don't produce water again.

(vi) Burning of wood:

  1. Wood changes chemically to carbon dioxide when it burns and leaves a residue of ashes.
  2. These ashes cannot be changed back to wood. So it is a chemical change.

The physical changes are

(vii) Boiling of water:

During boiling, water changes from liquid to a gaseous state, and on cooling the gaseous state or vapours can be converted back to the water. So a new product is formed.

(viii) Melting of butter in a pan:

Melting of butter only changes the shape of butter from solid to liquid. On cooling, it can return to its original shape


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