Matter

Question 1

What are the characteristics of a molecule?

Answer 1

A. They are very small in size
B. They have space between them
C. They are in constant motion (they possess kinetic energy)
D. They attract each other

Question 2

What is the size of a molecule?

Answer 2

A molecule is nearly 10-10 meter.

Question 3

What is intermolecular space?

Answer 3

The space between the molecules is called intermolecular space. It is less in solids, more in liquids and most in gases.

Question 4

What kind of Motion do molecules possess?

Answer 4

In solids they vibrate in their mean position.
In liquids molecules are free to move within the boundary of the container.
In gases the molecules move randomly in the space that is available to them.

Question 5

What is intermolecular force?

Answer 5

The molecules exert a force of attraction on each other. This force is called intermolecular force.

Question 6

What is the force of cohesion?

Answer 6

The intermolecular force of attraction between the molecules of the same substance is called the force of cohesion.

Question 7

What is the force of adhesion?

Answer 7

The force of attraction between the molecules of two different substances are called force of cohesion.

Question 8

What are the properties which decide the state of a substance?

Answer 8

1. Intermolecular space.
2. Force of attraction between the molecules.
3. Kinetic energy of molecules due to their motion.

Question 9

What is the molecular model of Solids?

Answer 9

1. They are made of very small molecules which can assumed to be tiny rigid balls.
2. The intermolecular space is very small.
3. The molecules in a solid can only vibrate in their mean positions.
4. The molecules are closely packed due to the strong attractive forces between them.

Question 10

What is the Molecular Model of Liquids

Answer 10

1. Each liquid is made up of tiny molecules that are not in a rigid arrangement.
2. The intermolecular spaces in liquids are more than solids.
3. The liquid molecules can move about freely within the boundary of the vessel.
4. The molecules in liquid or less closely pot and their positions are not fixed this is because the intermolecular forces in the liquid are weak in comparison to that of a solid.

Question 11

What is the Molecular Model of Gases

Answer 11

1. Gases are made up of molecules which can be assumed to be homogenous and perfectly elastic balls.
2. The intermolecular space is quite large compared to that in liquids and solids.
3. The molecules and gas can move about free in the space available to them.
4. Their intermolecular force is very weak.

Question 12

What is the change of state?

Answer 12

The process of change from one state to another either by absorption or rejection of heat at a constant temperature is called change of heat.

Question 13

What is Melting?

Answer 13

The change from solid to liquid on heating at a fixed temperature is called melting.

Question 14

What is the melting point of a solid?

Answer 14

The temperature at which is solid changes into liquid without further increase in temperatures called the melting point of the solid.

Question 15

What is freezing?

Answer 15

The change of a stage of a substance from the liquid state to a solid state on cooling is called freezing.

Question 16

What is the freezing point of a liquid?

Answer 16

The temperature at which a liquid changes into solid without further decrease in temperature is called the freezing point of the liquid.

Question 17

What is the molecular model of melting?

Answer 17

On heating a solid, the kinetic energy of molecules increases due to which they begin to vibrate violently. At a particular temperature, the molecules acquire sufficient kinetic energy to become far separated from each other by overcoming force of attraction.

Question 18

What is vaporization/boiling?

Answer 18

The change from liquid state to gaseous state on heating at a constant temperature by absorption of heat is called vaporization or boiling.

Question 19

What is the boiling point of the liquid?

Answer 19

The temperature at which a liquid changes into vapor without further increases in temperature is called the boiling point of liquid.

Question 20

What is evaporation?

Answer 20

The change of state from liquid to vapor at all temperatures from the surface of a liquid is called evaporation.

Question 21

What is the difference between boiling and evaporation

Answer 21

1. Evaporation is a slow process while boiling is a rapid process.
2. Evaperation takes place throughout the surface of a liquid while boiling takes place throughout the mass
   of a liquid.
3. Evaporation takes place at all temperatures while boiling takes place at a specific constant temperature.
4. In evaporation the temperature of the surroundings falls while in boiling the temperature of the surroundings remains constant

Question 22

What is the Molecular Model of Vaporization?

Answer 22

On heating the average kinetic energy of molecules of liquid increases. At a particular temperature the molecules receive sufficient kinetic energy to overcome the forces of attraction between themselves and they become free to leave this liquid surface.

Question 23

Explain the Molecular Model Evaporation.

Answer 23

Due to collision some molecules below the surface of liquid require sufficient kinetic energy to overcome the force of attraction and their inter-molecular space increases such a molecules move to the surface of the liquid and they absorb the heat from the surroundings to escape out into the atmosphere.

Question 24

What is Sublimation?

Answer 24

Sublimation is the process by which a solid when heated directly changes into vapor (gaseous state) without first changing into liquid.

Question 25

What is Deposition?

Answer 25

Deposition is the process when a vapor or gas on cooling changes directly into a solid without first changing into liquid.

Question 26

Explain the molecular model of sublimation.

Answer 26

In some solids the intermolecular forces of attraction are weak and on heating the molecules acquire sufficient kinetic energy to overcome the force of attraction. Thus their intermolecular separation becomes very large and they change into vapor directly.