1. Write a short note on chemical change.
2. Are tearing and burning of a piece of paper similar changes. If not, explain?
3. Explain combination reaction by taking an example.
4. Differentiate between combination reaction and displacement reaction.
5. What is neutralization reaction? Explain with the help of an example.
6. Explain the kind of change and reaction taking place when baking soda is added to vinegar.
Answers
Answer:
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Answer:
Question 1:
Which of these is a chemical change?
(a) A substacne with different chemical properties is formed.
(b) A substance in a different state but similar chemical properties is formed.
(c) The molecules of the substances do not undergo any change.
(d) A substance with a different shape and size but similar chemical properties is formed.
ANSWER:
(a) A substance with different chemical properties is formed.
A chemical change occurs when two substances react chemically to form new substances with different chemical properties.
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Question 2:
Which of these is an irreversible physical change?
(a) rusting of iron
(b) freezing of water
(c) a double decomposition reaction
(d) breaking of a glass tumbler
ANSWER:
(d) breaking of a glass tumbler
Breaking of a glass tumbler is an irreversible physical change. Rusting of iron is a chemical change. Freezing of water is a reversible physical change. A double decomposition reaction is a chemical change.
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Question 3:
An arrow pointing downwards in a chemical reaction shows
(a) evolution of gas
(b) formation of precipitae
(c) oxidation
(d) displacement
ANSWER:
(b) formation of precipitate
In a chemical reaction, an arrow pointing downwards shows the formation of a precipitate and an arrow pointing upwards shows the evolution of a gas.
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Question 4:
A chemical reaction in which heat is given out is called
(a) exothermic reaction
(b) endothermic reaction
(c) decomposition reaction
(d) neutralization reaction
ANSWER:
(a) exothermic reaction
Exothermic reactions are accompanied with release of heat. Endothermic reactions are accompanied with absorption of heat.
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Question 5:
In a combination reaction how many products are formed?
(a) two only
(b) one or two only
(c) one only
(d) number cannot be specified
ANSWER:
(c) one only
In a combination reaction, a compound is formed from its elements. For example, water and oxygen combine to form water.
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Question 6:
What happens in a displacement reaction?
(a) A more reactive element replaces a less reactive element.
(b) A less reactive element replaces a more reactive element.
(c) An element replaces one which is equally reactive.
(d) Any element can replace any other element with no relation to reactivity.
ANSWER:
(a) A more reactive element replaces a less reactive element.
In a displacement reaction, a more reactive element replaces a less reactive element from its compound.