18. There are many chemical changes taking place in our daily life. The milk turns sour, when it is placed for a long time at room temperature. Rusting of iron, melting of candle wax, all are examples of chemical changes. All these chemical changes occur due to chemical reactions, which changes the nature and the properties of the substances involved in these reactions. Some chemical reactions are beneficial, but some are harmful.
(i) "Many combustion reactions are combination reactions." Justify the statement by giving any two examples.
(ii) 'Should we use fire cracker during Diwali ? Comment on the statement by giving two valid reasons.
CBSE Class X Science SA 2 (3 Marks)
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(i) In combination reaction, two or more substances simply combine to form a new substance.
Combustion reaction is a reaction in which a substance reacts with oxygen to give a products.
C(s) + O2(g) → CO2(g)
2Mg(s) + O2(g) → 2MgO(s)
(ii) Use of fire crackers on Diwali or any other occasion should be avoided because : (a) exothermic reaction takes place, which liberates a huge amount of energy enhancing global warming.
(b) smoke causes air pollution.
(ii) Use of fire crackers on Diwali or any other occasion should be avoided because : (a) exothermic reaction takes place, which liberates a huge amount of energy enhancing global warming.
(b) smoke causes air pollution.
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Answer:
(i) In combination reaction, two or more substances simply combine to form a new substance. Combustion reaction is a reaction in which a substance reacts with oxygen to give a products. C(s) + O2(g) → CO2(g) 2Mg(s) + O2(g) → 2MgO(s)
(ii) Use of fire crackers on Diwali or any other occasion should be avoided because : (a) exothermic reaction takes place, which liberates a huge amount of energy enhancing global warming.
(b) smoke causes air pollution
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