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Explain the following: 

1. Ice floats over water. 

2. Dry ice sublimes. 

3. Two cubes of ice are pressed hard between the palm when the pressure is released the two cubes join together. 

4. The temperature of the water does not change once the boiling starts, in spite of the heat being supplied.

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1. Ice has an open cage, like structure due to which its volume increases and density decrease. Therefore it floats over water. 

2. The vapour pressure of dry ice becomes equal to the atmospheric pressure much before its melting point and hence it sublimes. 

3. When pressure is applied to ice cubes, the freezing point decreases. As a result, some of the ice in between the two cubes melts. The energy needed for melting is taken from the surroundings. Hence, when pressure is released, then the two cubes join together. 

4. The heat supplied at the boiling point of a liquid is used up in overcoming the forces of attraction between the particles of a liquid, during the change of liquid state to gaseous state without increasing their kinetic energy. Thus, the temperature remains constant.

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