# Selina Concise Class 6 Physics Chapter 1 Matter Solution

### (1) Write true or false for each statement:

(a) The molecules of each substance are identical

Ans:- (F)

(b) The inter – molecules forces are effective at all distance between the two molecules

Ans:- (F)

(c) The molecules in a substance are in random motion

Ans:- (T)

(d) In a gas, the molecules can move anyone in shape.

Ans:- (T)

(e) The liquids are less viscous than the gases

Ans:- (F)

### (2) Fill in the blanks:

(a) All the molecules of a substance are ………………..

Ans:- Identical

(b) The inter-molecular spacing is ……………. In solids …………. In liquids and ……………. In gases

Ans:- Least, more,  still more.

(c) The molecular motion liquids and gas is in …………. Path.

Ans:- zig-zag

(d) In  a solid, the molecules……………..  but they remain at their fixed positions.

Ans:-  vibrate  on either side

(e) the inter- molecules forces ate the weakest in ……………

(f) a solid extra pressure …………..

Ans:- gases

(g)  The Gases are  ………………. dense.

Ans:- least

(f) A solid is …………….. rigid

Ans:- most

### (3) Select the correct alternative:

(a) The diameter of a molecules is approximately

(i) 1 cm

(ii) 10 cm

(iii) 1—10m

(iv) 1 m

Ans:- (i) 1 cm

(b) The inter-molecules forces arte strongest in

(i) solids

(ii) liquids

(iii) gases

(iv) both (i) and (ii)

Ans:- (i) solids

(c) The molecules

(i) in solid, liquid and gas, move freely anywhere

(ii) in a solid, move freely within its boundary.

(iii) in a liquids, move within its boundary.

(iv) in a gas , move only within its boundary

Ans:- (iii) in a liquids, move within its boundary.

(d) The solids are

(i) more dense

(ii) less dense

(iii) least dense

(iv) highly compressible

Ans:- (i) more dense

(e) The inter-molecules forces in liquids are

(i) as strong as in  liquids

(ii) stronger than in solids

(ii) weaker than In solids

(iv) weaker than in gases

Ans: – (ii) weaker than In solids

### (4) Match the following columns:

Column A                                             Column B

(a) A molecule is composed of                    (i) does not exist free in nature

(b) Ice, water and water vapour                 (ii) can vibrate only up to about 10-10 m from their mean positions.

(c) An atom                                                  (iii) atoms.

(d) Gases                                                     (iv) are the three state of water

(e) The molecules                                        (v) occupy space of a solid

Ans:-

Column A                                             Column B

(a) A molecule is composed of                   (iii) atoms.

(b) Ice, water and water vapour                 (iv) are the three state of water

(c) An atom                                                 (i) does not exist free in nature

(d) Gases                                                    (v) occupy space of a solid

(e) The molecules                                       (ii) can vibrate only up to about 10-10 m from their mean positions.

### Short / Long answer questions:

(1) Define matter. What is its composition?

Answer: Matter is defined as anything which occupies space and has mass. It can be perceived by our senses of smell, touch, sight, hearing and taste.

Matter is made up of five elements: sky, air. fire, water, and earth.

(2) Name the three states of matter.

Ans. The three states of matter are – Solid, Liquid and Gas.

(3) What is a molecule?

Answer: A molecule is made up of one or more than one atoms of the same kind or of different kinds. A molecule can exist free in nature.

(4) What is the approximate size of molecules?

Ans. The approximate size of molecule is 10-9 m.

(5) One litre of water has 6.02 x 1026 molecules. Estimate the size of a molecule.

Answer: The size of a molecule of matter is very small. 1 litre (= 10-3 m3) of water has 6.02 x 1026 molecules, so the volume of a particle of water is

= 1.6 x 10-30 m3

r3 = 1.6 x 10-30 m3

Therefore, r = 0.725 x 10-10 m

(6) What do you mean by intermolecular spacing?

Answer: The spacing between particles of matter is called inter-molecular space.

(7) Describe a simple experiment to illustrate the existence of inter-molecular spacing.

Answer: It is easy to move the hand through water but difficult to move the hand in glycerine. The reason is that the attractive intermolecular forces are more in glycerine than in water.

(8) What do you mean by inter-molecular forces?

Answer: The force of attraction between the constituent particles is called the inter molecular force attraction.

(10) State three characteristics of molecules of matter which determine its solid, liquid and gaseous state.

Answer: Three characteristics of molecules of matter which determine its solid, liquid and gaseous state are

Solid: The molecules in a solid are closely packed.

Liquid: The molecules in a liquid are loosely packed.

Gases: The molecules in a gas are wide apart.

(11) State the approximate spacing between two molecules of a matter.

(12) How do solids, liquids and gases differ in their following properties:

(a) Size

(b) Shape

(c) Density?

 Solid Liquid Gas Size A solid has a definite size. A liquid has no definite shape A has neither a definite shape. Shape A solid has a definite shape. Acquires the shape of the container. Acquires the shape of the container. Density High Density Low Density Low Density

(13) The molecules in a substance are in motion. What type of path do they follow?

Ans: The attractive force between the molecules of a liquid is not as strong as it in solids, so they are loosely packed and are not fixed. The molecules can move over one another, within the boundary of the liquid.

(14) Describe a simple experiment to illustrate that molecules are not at rest, but they constantly move.

Ans. Take a beaker. Fill it partly with water. Add some lycopodium powder in the beaker containing water. Stir the contents of the beaker with a glass rod. Take out few drops of the suspension on a glass plate. Place the plate on the table and illuminate it with a table lamp. Observe the glass plate through a microscope. It is found that the fine particles of lycopodium powder move rapidly in a random manner and their path is zig zag.

The reason is that the particles of water are in random motion which collide with the suspended fine particles of lycopodium powder and make them to move in a zig zag path.

(15) Write down five general properties of solids, liquids and gases.

Ans. The five general properties of each solids, liquids and gas are as follows:

Properties of solids:

(i) A solid has a definite shape and size.

(ii) A solid can not be compressed.

(iii) A solid can not flow.

(iv) A solid is highly dense.

(v) A solid has its constituent molecules very closely packed.

Properties of Liquids:

(i) Liquids have a definite volume, but no definite shape because they acquire the shape of the container in which they are kept.

(ii) Liquids are almost incompressible.

(iii) Liquids can flow.

(iv) Liquids have only one free surface.

(v) Liquids are less rigid.

Properties of Gases

(i) A gas has neither a definite shape nor a definite volume. It acquires the shape and volume of its container.

(ii) Gases are highly compressible.

(iii) Gases can flow. They are also viscous, but less viscous than liquids.

(iv) Gases are not rigid.

(v) A gas has no free surface.

(16) Give the molecular model for a solid and use it to explain why a solid has a definite volume and a definite shape.

Ans. The answer are point wise below:

(i) There is a strong force of attraction (strong inter-molecular force) between the molecules of a solid.

(ii) The molecules in a solid are closely packed, i.e. inter – molecular space is negligible. Therefore, solids cannot be compressed much. The molecules are arranged in a definite manner, therefore they have a definite shape.

(iii) The molecules vibrate on either side of their mean positions but they do not leave their positions. Therefore solids have a definite size.

(iv) The molecules of a solid are arranged in a definite manner. They are packed tightly packed and so they generally have a high density.

(17) Describe the molecular model for a liquid. How does it explain that a liquid has no definite shape, but has a definite volume?

Ans. Molecular Model for a Liquid:

(i) The attractive force between the molecules of a liquid is not as strong as it is in solid, so they are loosely packed and are not fixed. The molecules can move over one another within the boundary of the liquid. Thus a liquid has a definite volume, but no definite shape.

(ii) The inter-molecular space in a liquid is greater than in a solid, so they generally have low density as compared to a solid i.e. they are more compressible.

(iii) The motion of molecules in a liquid is irregular and random within the boundary of the liquid.

liquid has no definite shape, but has a definite volume: Liquids do not have a definite shape, but have a definite volume and can flow from a higher to a lower level. They show the property of viscosity and surface tension because of the cohesive forces.

(18) A gas has neither a definite volume nor a definite shape. Describe the molecular model to explain it.

Ans. Molecular Model of Gases, neither a definite volume nor a definite shape:

(i) The molecular of a gas lie much farther apart than they lie in a liquid or a solid. Thus the density of gases is very low.

(ii) There is negligible force of attraction between the molecules of a gas, so they are free to move in the entire space available to them.

(iii) The molecules of a gas move much faster than they move in liquids and therefore they are infact in a state of incessant random motion, moving in all possible speeds.

(iv) The molecules of a gas are far apart and there is enough space available for compression. Thus gases can easily be compressed.

(v) During motion the molecules of a gas collide with one another and also with the wall of the vessel. In each collision, the direction of motion of the molecule changes so the momentum changes.

(vi) A gas exerts pressure on the wall of its container due to the continuous collisions of its molecules with the wall.

(19) Distinguish between the three states of matter – solids, liquid and gas on the basis of their molecular models.

Ans. The difference between solid, liquid and gas are following:

 Solids Liquids Gases (i) A solid has a definite shape and a definite size. (i) A liquid has a definite volume but not a definite shape. (i) A gas has neither a definite volume nor a definite shape. (ii) The molecules in a solid are closely packed. (ii) The molecules in a liquid are loosely packed. (iii) The molecules in a gas are wide apart. (iii) The molecules in a solid are fixed at their positions. They can only vibrate about their mean positions. (ii) The molecules in a liquid can move within the boundary of the liquid. (iii) The molecules of a gas can move freely in space (iv)  The intermolecular forces are strong. (ii) The intermolecular forces are less strong. (iii) The intermolecular forces are weak.

(20) Distinguish between solids, liquids and gases on the basis of their following properties.

(a) compressibility

(ii) fluidity

(iii) rigidity

(iv) expansion on heating

 Solid Liquid Gas Compressibility Not Compressible Negligibly compressible Highly compressible Fluidity Not possible Can flow Can flow Rigidity Highly rigid Less rigid Not rigid Expansion on heating Low Expansion on heating in liquid is more than solids. Expansion on heating in gas is more than liquids.

(21) What do you mean by change of state of matter? Explain:

(a) the change of a solid into a liquid at a constant temperature, and

(b) the change of a liquid into a gas at a constant temperature.

Ans. Change of state of matter:

The change in state of matter of a substance from solid to liquid or from liquid to gas is brought about by imparting heat energy to it at a constant temperature.

Change of a Solid into a Liquid at a Constant Temperature:

The changing process of a substance from solid to liquid state on absorption of heat at a particular temperature, called the melting point is called melting or fusion. The heat energy absorbed by the substance increases the amplitude of vibrations of the molecules of the solid and a stage is reached at the melting point when the molecules acquire sufficient energy to overcome the force of attraction between them become free to move. The solid thus changes into a liquid.

Change of a liquid into a gas at a constant temperature:

The process of change of a substance from the liquid state to its gaseous state at a particular temperature, called the boiling point. The heat energy absorbed by a substance in liquids state increases the energy of its molecules due to which they begin to move randomly. Thus a liquid changes into a gas.           Updated: March 11, 2020 — 2:55 pm