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DAV Class- 6 Changes Around Us Question and Answer
Something To Know
A. Fill in the blanks.
1. All irreversible changes bring a permanent change in a substance.
2. A change, in which the substance produced can get back to the original form, is called a reversible change.
3. Bending of an iron rod is a physical change.
4. Burning of fuel is a fast chemical change, whereas rusting of iron is a slow chemical change.
5. In chemical change, new substances with different properties are formed.
B. Write True or False for the following statements.
1. Glowing of an electric bulb is a fast change.
Answer 1: True
2. Deforestation is a reversible change.
Answer 2: False
3. Burning of paper is a temporary change.
Answer 3: False
4. Cutting of an apple is a chemical change.
Answer 4: False
5. Making of fruit salad is a chemical change.
Answer 5: False
6. Changing milk into curd is a physical change.
Answer 6: False
C. Tick the correct option.
1. Which of the following can be considered as a fast change?
Answer 1: bursting of a firecracker
2. Evaporation of water is a-
Answer 2: physical change
3. Which one of these changes is a reversible change?
Answer 3: inflating a balloon
4. Which one these is an irreversible change?
Answer 4: growth of a child
5. A piece of paper undergoes a chemical change when it is-
Answer 5: burned
D. Answer the following questions in brief.
1. Define the following terms.
(a) Reversible change
(b) Chemical change
(c) Physical change
Answer 1:
(a) Reversible change – a change, in which substance produced, can be brought back into its original form.
(b) Chemical change – a change, in which a new substance, is formed.
(c) Physical change – a change, in which no new substance, is formed.
2. Distinguish between fast and slow changes. Give two examples of each type.
Answer 2:
Fast changes – The changes, that take place quickly, or in a shorter duration of time, are called fast changes.
Two examples of fast changes are: burning of paper and the lighting of a bulb.
Slow changes – The changes, that take place in a longer duration of time, are called slow changes.
Two examples of slow changes are the change of seasons and the growth of a plant.
3. Give two examples each of reversible and irreversible change.
Answer 3: Examples of reversible change- freezing of ice and the melting of wax.
Examples of irreversible change- burning of wood and making of curd from milk.
4. State some of the irreversible biological changes that take place in nature.
Answer 4: Germinating of seed, Ripening of fruits, growth of a child are some of the irreversible biological changes that take place in nature.
5. Give one example of a physical change in which (i) energy is given out (ii) energy is absorbed.
Answer 5: (1) glowing of bulb.
(2) melting of ice.
E. Answer the following questions.
1. Give two differences between reversible and irreversible changes.
Answer: two differences between reversible and irreversible changes are-
Reversible Change:
1. A reversible change is one in which the substance produced can be returned to its original state.
2. These are temporary changes that can be reversed once the actual cause is removed. Example: melting of ice
Irreversible Change:
1. An irreversible change is one in which the substance produced cannot be returned to its original state.
2. These are irreversible changes that cannot be reversed even if the cause of the change is eliminated. Example: Making curd from milk.
2. ‘Formation of curd is an irreversible as well as a chemical change.’ Justify this statement.
Answer 2: Curd formation is an irreversible process because curd cannot be converted back to milk. It’s also a chemical change because a new substance, curd, is formed with different properties.
3. Water cycle is a natural change. Classify it as a (i) physical or chemical change (ii) a reversible or irreversible change. Also, justify your answer.
Answer 3:
(1) The water cycle is both a natural and physical change because no new substance is generated; only the appearance and physical state are changed.
(2) The water cycle is a natural transformation that is also reversible because water changes from a liquid to a vapour state and then back to a liquid state.
4. How can we say that burning of candle is a chemical change but the glowing of bulb is a physical change?
Answer 4: We can say that burning a candle is a chemical change since it produces light, heat, and smoke, all of which are new properties. The lighting of a bulb, on the other hand, is a physical change because no new substance is generated; just the look of the bulb changes. As a result, we can define it as a physical change.