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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 as chemical or physical change:
Cutting of trees
Match the columns
| column A | coulmn B |
| 1. A change which cannot be easily reversed | a. man-made change |
| 2.A change that repeats itself at regular intervals | b. chemical change |
| 3. A change that is made by humans | c. physical change |
|
4. A change in which the original substance cannot be obtained |
d. periodic change |
| 5. A change where no new substance is formade | e. irreversible change |
| f. slow change |
Write true or false for the statement.
Burning of paper and formation of curd are reversible changes
Write short answer.
What are man-made changes ?
Tick (√) the correct alternative from the choice given for the following statement
A pop sound is heard when a lighted match stick is brought near the mouth of a jar. This indicates the release of gas.
Which of the following are physical changes and which are chemical changes?
Burning of candle wax, Melting of candle wax, Mixing of iron filings and sand, Burning of wood, Breaking a piece of chalk, Burning a piece of paper, Cutting a piece of paper.
Give three reasons why melting of wax, is considered a physical change while burning of a candle, a chemical change.
Select the chemical changes from the following list of changes
Rotting of eggs.
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 |
Give two examples for the following case:
Physical changes which are not reversible
