Option 3 : Both 1 and 2
The correct answer is 3 i.e. Both 1 and 2.
Concept:
Latent heat:
- The heat energy which has to be supplied to change the state of a substance is called its latent heat.
- Latent heat does not raise the temperature.
- But latent heat has always to be supplied to change the state of a substance.
- The word 'latent' means hidden.
- The latent heat which we supply is used up in overcoming the forces of attraction between the particles of a substance during the change of state.
- Latent heat is of two types:
- Latent heat of fusion
- Latent heat of vaporization
Explanation:
| Phenomenon |
Explanation |
| Latent heat of fusion |
- There is no rise in temperature during the melting of ice. Hence, Statement 1 is correct.
- The heat which is going into ice but not increasing its temperature is the energy required to change the state of ice from solid to liquid.
- The heat energy is used up in changing the state of the solid substance by overcoming the force of attraction between its particles.
- Ice at 0°C is more effective in cooling a substance than water at 0°C. Hence, Statement 2 is correct.
- When a liquid freezes to form a solid, an equal amount of heat is given out.
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| Latent heat of vaporization |
- Once the water has begun to boil, the temperature remains constant at 100°C until all the water has changed into steam.
- The heat energy supplied to a boiling liquid is used up in changing the state of the liquid substance by overcoming the force of attraction between its particles.
- When water changes into steam, it absorbs latent heat, but when steam condenses to form water, an equal amount of latent heat is given out.
- The burns caused by steam are much more severe than those caused by boiling water.
- This is because steam contains more heat, in the form of latent heat than boiling water.
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