[5 Mark Question Answer]

Question 15 Marks

Demonstrate the process of boiling with the help of an activity.

Answer

The process of conversion of a liquid into its gaseous state, at a particular temperature, on heating is called boiling. The following activity demonstrates the process of boiling of water.
Materials required : A beaker filled with water, a thermometer, a clamp stand, a Bunsen burner, a tripod stand and a wire gauze.
Procedure :
Place the beaker filled with water on the wire gauze and the tripod stand. Suspend the thermometer with the help of the clamp stand and lower it into the beaker. Start heating the beaker with the help of Bunsen burner. Observed what happens to the water and record the temperature after every $30$ seconds.
Observations :
The temperature of the water rises till it reaches the temperature of $100 ^\circ C$.
The water starts getting converted to steam, when its temperature reaches $100 ^\circ C$.
The temperature recorded by the thermometer remains fixed at $100 ^\circ C$ till the water is completely converted into steam.
Conclusion :
When heat is supplied to water, the temperature of the water rises till it reaches $100 ^\circ C.$
The water then starts getting converted into steam at a constant temperature of $100 ^\circ C$. This process is known as boiling and the temperature of $100 ^\circ C$ is known as the boiling point of water.

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Question 25 Marks

Explain conduction of heat in solids on the basis of the kinetic theory of matter.

Answer

The mode of transfer of heat energy from one molecule to another molecule in the direction of heat flow, from higher temperature to lower temperature without actual movement of molecules from their mean position is called conduction.
According to kinetic theory of matter, when we heat some solid, the molecules get heat energy, the kinetic energy of molecules increases, they vibrate about their mean position with greater amplitude. As a result, the molecules collide with next molecules and transfer part of heat energy to them and so on. In this way, the heat gets transferred from hotter part to colder one.

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Question 35 Marks

State the main postulates of the kinetic theory of matter.

Answer

The main postulates of the kinetic theory of matter are as follows :
Matter is made up of very small particles called molecules which are in a state of constant motion. Due to this motion they posses kinetic energy.
The motion of particles and their kinetic energy is directly proportional to heat. When the substance is heated, the velocity of particles also increases. As a result their $\text{K.E}$. also increases and when the substance is cooled, it loses its heat and velocity of particles decreases. As a result, $\text{K.E}$. also decreases.
Molecules of matter always exert force of attraction on each other. This force of attraction is called intermolecular force of attraction.
Intermolecular force of attraction is inversely proportional to the intermolecular distance.

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Question 45 Marks

Explain the properties of liquids on the basis of kinetic theory of matter.

Answer

The properties of liquids are given below.
The molecules in a liquid are loosely packed. Therefore, intermolecular spaces in a liquid are more than that in a solid. Thus, the intermolecular force of attraction in a liquid is weaker as compared to that in a solid.
Because of the weak intermolecular force of attraction, molecules in a liquid can change their positions and can also slide oyer one another. This enables a liquid to flow. So, liquids do not have a definite shape, they take the shape of the container in which they are kept.
Although liquids do not have a definite shape, they have a definite volume. This is because there exists substantial intermolecular force of attraction, which holds the molecules together.
Liquids have larger intermolecular spaces than solids. Therefore, they may be compressed slightly.
On heating, liquids expand more than solids because of the weaker intermolecular force of attraction.

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Question 55 Marks

Describe the arrangement of molecules in the three different states of matter.

Answer

Arrangements of molecules in solids :
Molecules in solids are very tightly packed, thus the intermolecular spaces between them are very small. Hence, the intermolecular force of attraction is very strong in solids. The strong intermolecular force of attraction does not allow molecules in solids to move away from their fixed positions.

Arrangements of molecules in liquids :
The molecules in a liquid are loosely packed. Therefore, intermolecular spaces in a liquid are more than that in a solid. Thus, the intermolecular force of attraction in a liquid is weaker as compared to that in a solid. Because of the weak intermolecular force of attraction molecules in a liquid can change their positions and can also slide over one another.

Arrangements of molecules in gas :
The intermolecular spaces in a gas are very large as compared to that in a solid or a liquid.
Thus, the intermolecular force of attraction is negligible in a gas. Due to this negligible intermolecular force of attraction, molecules in a gas are able to move independently and occupy the entire space in a container.

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