10th Class Physical Science - Question Bank
Why do we get dew on the surface of a cold soft drink bottle kept in open air?
The temperature of the cold soft drink bottle is less than the temperature of atmosphere. The water molecules present in air touches the surface of the bottle and lose their kinetic energy. As a result the temperature of water molecules decrease and condenses on the surface of the bottle. These water droplets are seen as dew.
Write the differences between evaporation and boiling.
Evaporation : The process of escaping of molecules from the surface of a liquid at any temperature is called evaporation. Evaporation is a cooling process. It is a surface phenomenon. Boiling : The process in which the liquid phase changes to gaseous phase at a constant temperature and pressure is called boiling. Boiling does not cause cooling. Boiling is a bulk phenomenon.
Does the surrounding air become warm or cool when vapour phase of H2O condenses? Explain.
Condensation is a warming process. The process of phase change of vapour to liquid is condensation. When vapour touches a cool object the molecules in vapour lose kinetic energy.
As a result the temperature of water molecules decreases and condenses on the surface of the cool object. This is an exothermic reaction. So the average kinetic energy of the molecules in vapour
increases. Thus the surrounding temperature increase.
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