Science

Physical and Chemical Changes

Question:

Explain why burning of wood and cutting it into small pieces are considered as two different types of changes. ~

Answer:

Burning of wood is a chemical change because in burning new substances are formed as
Wood + Oxygen ———–> Charcoal + Carbon dioxide + Heat + Light
But cutting it into small pieces is physical change because no new substance is formed. We can only reduce the size of wood.

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Physical and Chemical Changes

Q 1.

Explain why rusting of iron objects is faster in coastal areas than in deserts.

Q 2.

How would you show that setting of a curd is a chemical change?

Q 3.

Fill in the blanks in the following statements:
(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of .
(b) The chemical name of baking soda is .
(c) Two methods by which rusting of iron can be prevented are __________ and __________
(d) Changes in which only ____________ properties of a substance change are called physical changes.
(e) Changes in which new substances are formed are called _____________ changes..

Q 4.

Explain how painting of an iron gate prevents it from rusting?

Q 5.

Describe how crystals of copper sulphate are prepared.

Q 6.

Explain why burning of wood and cutting it into small pieces are considered as two different types of changes. ~

Q 7.

When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.

Q 8.

Explain why rusting of iron objects is faster in coastal areas than in deserts.

Q 9.

Classify the changes involved in the following processes as physical or chemical changes:
(a) Photosynthesis
(b) Dissolving sugar in water
(c) Burning of coal
(d) Melting of wax
(e) Beating aluminium to make aluminium foil
(f) Digestion of food

Q 10.

When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.

Q 11.

(a) Cutting a log of wood into pieces is a chemical change. (True/ False)
(b) Formation of manure from leaves is a physical change. (True/ False)
(c)Iron pipes coated with zinc do not get rusted easily. (True/ False)
(d)Iron and rust are the same substances. (True/ False)
(e)Condensation of steam is not a chemical change. (True/ False)