1. Differentiate between solids, liquids and gases on the basis of their molecular
models.
2.Explain the process of boiling on the basis of kinetic theory and also give the
boiling point of water in SI unit.
3.Explain the phenomenon of conduction and convection on the basis of kinetic
theory of matter.
4. Define the process of sublimation. Give two examples of substance which
sublimate at room temperature and two substances which sublimate on heating.
What is the reverse process of sublimation called?
5. Differentiate between evaporation and boiling.
6, Explain the cause of evaporation.
7. Give reasons for the following (a) Strips of wet cloth are put on the forehead of a
patient having fever. (b) Hot milk is poured in a saucer to cool it faster.
Answers
1. Solids have less intermolecular space and more intermolecular force. Liquids, compared to solids, have more intermolecular space and less intermolecular force. Hence making it a fluid. And gases, have the least intermolecular force and most intermolecular space. So, gases are fluids as well.
2. If more heat energy is supplied, the particles move fast enough, so they can break the bonds between them. Therefore, the liquid boils. Hence, the heat energy required to heat a liquid to a gas is called it's boiling point. It's boiling point is 373.15 K
3. Conduction occurs as rapidly moving or vibrating atoms and molecules interact with others. Hence, they transfer some of their kinetic energy. Convection is the motion of the fluid affected by temperature differences across the fluid. When fluids are heated, the region in closest contact with the heat source becomes less dense due to the high kinetic energy in the particles.
4. Sublimation is the direct change of a substance from the solid state to the gaseous state without undergoing the liquid state.
Example of substances which sublimate at room temperature: CO2, Iodine
Examples of substances which sublimate on heating: Camphor, Ammonium Chloride.
The reverse process of sublimation is called deposition.
5. Evaporation happens at the surface of the liquid, whereas boiling happens throughout the liquid. Evaporation happens slowly, while boiling is a fast reaction. Evaporation happens at any temperature but boiling happens at a fixed temperature called boiling point (100 °C or 373.15 K)
6. Heat is the cause of evaporation.
7.(a) Because the water in the cloth absorbs heat from the forehead to get vaporised. It helps to decrease fever
(b) When hot milk is put in a saucer, it's surface area in contact with air at room temperature increases. It helps in cooling of liquid by losing heat.