SELECT * FROM question_mgmt as q WHERE id=3969 AND status=1 SELECT id,question_no,question,chapter FROM question_mgmt as q WHERE courseId=8 AND subId=16 AND chapterId=181 and ex_no='5' AND status=1 ORDER BY CAST(question_no AS UNSIGNED) CBSE Free NCERT Solution of 9th science Is Matter Around Us Pure which of the following are chemical changes a

Question:

Which of the following are chemical changes?

(a) Growth of a plant
(b) Rusting of iron
(c) Mixing of iron filings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of a candle.

Answer:

(a). Growth of a plant is a chemical change because at the time of photosynthesis, plants convert sunlight into chemical energy and this is an irreversible process.

(b). Rusting of iron is a chemical change because there is formation of new substance i.e.- Fe2O3, xH2O (Rust).

(c). Mixing of iron filings and sand is a physical change process.

(d). Cooking of food in a chemical change because there is change in chemical composition by supplying heat in addition to some food additives, oil, butter etc.

(e). Digestion of food is à chemical change because the enzyme present in stomach are break large macromolecules into simple molecules.

(f). Freezing of water is a physical change. because there is change in physical state of water notinitis composition.

(g). Burning of a candle is a chemical change because there is emission of CO2 and water vapours during the burning of candles.


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