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प्रश्न
When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.
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उत्तर
- When a candle burns, the melting of wax is a physical change and the burning of the candle is a chemical change. When the wax melts, only its physical properties change.
- Hence, it is a physical change. When a candle burns, its chemical properties and composition change, the melted wax turns into carbon dioxide and other substances and it cannot be obtained in its original form.
- It is a chemical change. Hence, when a candle burns, both physical and chemical changes take place.
Example:
When coal is broken into pieces and burned, both physical and chemical changes occur. Breaking coal into pieces is a physical change. The properties of coal do not change in this. Burning of coal is a chemical change. Due to burning, the chemical properties of coal change and new substances are formed.
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संबंधित प्रश्न
Classify the following changes as physical or chemical.
Given reason:
Cutting of a cloth piece is a physical change, though it cannot be reversed.
Change is the law of nature and occurs in our everyday life, at all times and in all places. Differentiate between the following change with a suitable example.
Desirable and undesirable change.
State why addition of sodium chloride to water is considered a physical change, while addition of dilute sulphuric acid to zinc is considered a chemical change.
Give a reason why
Change of seasons is a periodic change while the change of weather is a non-periodic change.
Name the following.
The product obtained during a physical change when water converts from a liquid into a solid.
You are given some candle wax. Can you make a candle doll from it? What kind of change is this?
Two drops of dilute sulphuric acid were added to 1 g of copper sulphate powder and then small amount of hot water was added to dissolve it (step I). On cooling, beautiful blue coloured crystals got separated (step II). Step I and Step II are:
State whether the following statement is true or false:
Stretching of rubber bands is not a physical change.
Match the items of Column I with the items of Column II.
| Column I | Column II | ||
| (a) | Large crystals | (i) | Turns lime water into milky |
| (b) | Depositing a layer of zinc on iron | (ii) | Physical change |
| (c) | Souring of milk | (iii) | Rust |
| (d) | Carbon dioxide | (iv) | Sugar candy (Mishri) |
| (e) | Iron oxide | (v) | Chemical change |
| (f) | Dissolving common salt in water | (vi) | Galvanisation |
