Cordova book solutions of Class 6 science chapter 6 Changes around us
Today, I am sharing Class 6 science chapter 6 Changes around us. Hope it helps!
Class 6 science chapter 6 Changes around us
Very short answer questions
1. What kind of change is burning of paper?
ANSWER: Burning of paper produces new substance such as carbon dioxide gas, ash etc. It is irreversible and permanent change. Thus, it is chemical change.
2. What happens when an aluminium rod is heated?
ANSWER: When an aluminium rod is heated it bring change such as it expands.
3. What happens on cooling of steam?
ANSWER: On cooling of steam, it changes into water and it is a condensation process.
4. What type of change is melting of wax?
ANSWER: The melting of wax do not produce new substance as it solidifies again. It is reversible and temporary change. Thus, it is physical change.
5. Is the formation of day and night, a natural or human-made change?
ANSWER: The formation of day and night is a natural change.
6. What change do you observe on applying pressure on brittle substances?
ANSWER: When we apply pressure on brittle substances, they break into pieces that cannot be reversed. Thus, it is an irreversible change.
Short answer questions
1. What are reversible changes?
ANSWER: The changes that can be reversed by reversing the conditions to obtain a substance in its original form. For example: Ice changes into water by melting and by cooling water reversed to form ice.
2. What are irreversible changes?
ANSWER: The changes that cannot be reversed even by reversing the conditions to obtain substaance back in its original form. For example: raw egg to boiled egg is irreversible change as boiled egg cannot be reversed to raw egg.
3. Neha’s mother is sick. Neha makes vegetable soup for her mother and serves it to her.
(a) Can we get the vegetables back from the soup? What type of change does it represent?
ANSWER: No, we cannot vegetables back from soup as it represents irreversible change.
(b) What value does Neha’s action show?
ANSWER: Caring daughter
4. What are the different ways to bring about changes?
ANSWER: Different ways to bring about changes are: Heating or cooling, Applying pressure and by mixing two or more things together.
5. What change do you observe on keeping milk in refrigerator?
ANSWER: We keep milk in refrigerator for cooling, to stay longer and to not get spolied.
6. Classify the following as reversible or irreversible changes: burning of coal, freezing of water, digestion of food, ironing of a shirt, baking of a chapati, knitting of a sweater, folding of paper and rusting of iron
ANSWER: Reversible change – freezing of water, ironing of a shirt, knitting of a sweater, and folding of paper. Irreversible change – burning of coal, digestion of food, baking of chapati and rusting of iron.
Long answer questions
1. Explain how heating or cooling of water brings change in the state of matter.
ANSWER: Heating or cooling brings change in the states of matter as:
a) Certain things become hot on heating cool on cooling. For example: by keeping water in refrigerator, water becomes cold. In nature also, days are warm because of heating if sun and nights are cool because there is no sun.
b) Certain things become expand on heating and contract on cooling. For example: Iron or aluminium become expand on heating and contract on cooling.
2. Explain how a metal rim is fixed around the wooden wheel of cart.
ANSWER: Metal rim fixed on the wooden wheel of cart by heating or cooling. On heating, metal such as iron expand and easily put around the wooden wheel. Then it cools and on cooling, it contracts and metal rim will be tightly fit around the wooden wheel of cart.
3. How are physical changes different from chemical changes?
ANSWER: Physical changes is a change in which no new substance is formed. It is reversible and temporary change. For example, tearing of paper.
Chemical change is a change in which new substance is formed. It is irreversible and permanent change. For example, burning of paper.
4. Is the burning of a candle a chemical or physical change? Explain with reasons.
ANSWER: Burning of candle is a chemical change. Chemical change is a change in which new substance with different properties are formed. It is irreversible and permanent change. On burning candle, wax burns to produce wax vapour and carbon dioxide gas which is a new substance and that cannot be reversed.
HOTS (Higher Order Thinking Skills) questions:
1. Why is gap left between the rails in railway tracks?
ANSWER: Gap left between the rails which is made of metal in railway tracks. This is because in summers changes such as metal expansion takes place. Metal expands in summers and contract in winters. If there is no gap left then on expansion, there will be bend in rails and accident may took place.
2. Why is mercury used in thermometers?
ANSWER: Mercury is the only metal which is liquid at room temperature. The mercury expands and contracts on changing temperature because it has high coefficient of expansion.
3. What is the difference between the following changes:
(a) Rolling of roti from dough
ANSWER: Rolling of roti from dough results in no formation of new substance. It can be reversed and temporary change. Thus, it is a physical change.
(b) Baking of roti
ANSWER:Baking of roti results in formation of new substance. It cannot be reversed and permanent change. Thus, it is a chemical change.
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