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Question
Describe an experiment to demonstrate that water absorbs heat during boiling at a constant temperature.
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Solution
BOILING POINT OF WATER AT CONSTANT TEMPERATURE:
Take some water in a beaker. Suspend and clamp a thermometer in a beaker in water so that the bulb of thermometer remains in water without touching bottom and sides of the beaker. Supply heat by the burner and note the temperature at room temperature (20°C nearly)
Record the temperature after every minute. The temperature rises and as it reaches 100°C water starts boiling. Though heat is being supplied temperature does not rise i.e. it remains constant at 100°C and bubbles formed are seen. Thus, the boiling point of water is 100°C and at boiling point heat supplied is absorbed by water at a constant temperature. Because this heat is being used to change every molecule of water into vapours.
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RELATED QUESTIONS
State the boiling point of water.
A certain quantity of water is heated from 20°C to 100°C. Its temperature is recorded after each 1 minute. The observations are:
| Time (in minute) | Temperature (in °C) |
| 0 | 20 |
| 1 | 30 |
| 2 | 40 |
| 3 | 50 |
| 4 | 60 |
| 5 | 70 |
| 6 | 80 |
| 7 | 90 |
| 8 | 100 |
| 9 | 100 |
| 10 | 100 |
| 11 | 100 |
| 12 | 100 |
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