Selina Concise Class 8 Physics Solution Chapter No. 1- ‘Matter’ For ICSE Board Students.
Selina Concise Physics Solutions for Class 8th Chapter 1 Matter with easy language, expert answers and doubt clearing sections. The book is especially designed keeping in mind the syllabus of ICSE board and the difficulty level faced by the students of ICSE boards Class 8.
Selina Class 8 Physics Solution Chapter 1:
1.) Write true or false for each statement :
a) The temperature of a substance remains unaffected during its change of state.
Answer: True.
Temperature does not changes while state of change.
b) Ice melts at 100⁰ C.
Answer: False.
Ice melts from 0⁰ C.
c)Water at 100⁰ C has more heat than steam at 100⁰ C.
Answer: False.
Water and steam possesses same energy. This heat is supplied by surrounding of the object.
d) Evaporation of a liquid causes cooling.
Answer:True.
Heat requires for evaporation process. This heat is supplied by surrounding of the object. Thus heat produces cooling effect.
e) Water evaporates only at 100⁰C.
Answer: False.
Evaporation process does not requires fixed temperature. It may occur at any temperature
f) Boiling takes place at all temperatures.
Answer: False.
The process of boiling is done at particular temperature only.
g) Evaporation takes place over the entire mass of the liquid.
Answer: False.
Evaporation takes place at the surface of substance only.
h) The process of a gas converting directly into solid is called vaporization.
Answer: False.
The process of a liquid converting into vaporis called vaporization. The process of conversion of gas into solid is called condensation.
i) At high altitudes, water boils above 100⁰ C.
Answer: False.
Boiling point does not depend on temperature of surrounding.
j) The melting point of ice is O⁰ C.
Answer: True.
Ice melts and converts into liquid from 0⁰ C.
2.) Fill in the blanks:
a) Evaporation takes place at ……. temperatures.
b) ……… process is just the reverse of melting.
c) ………. is a process that involves direct conversion of a solid into its vapour on heating.
d) The temperature at which a solid converts into a liquid is called its ……..
e) The smallest unit of matter that exists freely in nature is called ……..
f) Molecules of a substance are always in a state of ….. and so they possess……..
g) Inter-molecular space is maximum in …… less in …… and the least in ……
h) Inter-molecular force of attraction is maximum in ……, less in …….. and the least in ……….
Answer:
a) Evaporation takes place at all
b) Freezing process is just the reverse of melting.
c) Sublimation is a process that involves direct conversion of a solid into its vapour on heating.
d) The temperature at which a solid converts into a liquid is called its melting
e) The smallest unit of matter that exists freely in nature is called molecule.
f) Molecules of a substance are always in a state of motion and so they possess kinetic energy.
g) Inter-molecular space is maximum in gases less in liquid the least in solid.
h) Inter-molecular force of attraction is maximum in solid, less in liquid and the least in gases.
3.) Match the following :
Column A Column B
(a) Molecules (i) water boils
(b) 100⁰C (ii) evaporation
(c) 0⁰ C (iii) changes from solid to gas
(d) At all temperatures (iv) matter
(e) Camphor (v) water freezes
Answer:
Column A Column B
(a) Molecules (iv) matter
(b) 100⁰C (i) water boils
(c) 0⁰ C (v) water freezes
(d) At all temperatures (ii) evaporation
(e) Camphor (iii) changes from solid to gas
4.) Select the correct alternative:
a) The inter-molecular force is maximum in
(i) solids
(ii) gases
(iii) liquids
(iv) none of the above.
Answer: (i) solids
The molecules binds each other by molecular force in solids.
b) The inter-molecular space is maximum in:
(i) liquids
(ii) solids
(iii) gases
(iv) none of the above.
Answer: (iii) gases
Molecules are far from each other in gases than liquid and solids.
c) The molecules can move freely anywhere in :
(i) gases
(ii) liquids
(iii) solids
(iv) none of the above.
Answer: (i) gases
Inter-molecular force does not bind molecules in gases therefore the can move freely anywhere.
d) The molecules move only within the boundary in:
(i) liquids
(ii) gases
(iii) solids
(iv) none of the above.
Answer: (i) liquids
The inter-molecular force is between solid and gases. Molecules can moves only within boundaries in liquid.
e) The temperature at which a liquid gets converted into its vapour state is called its:
(i) melting point
(ii) boiling point
(iii) dew point
(iv) freezing point
Answer: (ii) boiling point
Liquids converts into vapour at boiling temperature.
f) Rapid conversion of water into steam is an example of :
(i) evaporation
(ii) freezing
(iii) melting
(iv) vaporization.
Answer: (iv) vaporization.
Vaporization is a rapid process.
g) Evaporation takes place from the :
(i) surface of liquid
(ii) throughout the liquid
(iii) mid-portion of the liquid
(iv) bottom of liquid.
Answer: (i) surface of liquid
Evaporation takes place at only surface of the liquid.
h) Boiling takes place from :
(i)the surface of the liquid
(ii) throughout the liquid
(iii) mid-portion of liquid
(iv) none of the above.
Answer: (ii) throughout the liquid
Boiling takes place throughout the liquid. All molecules vibrates with same kinetic energy.
B.) Short/Long Answer Questions :
1) Define the term matter. What is it composed of ?
Answer:
Matter is nothing but something which can be perceived by our sense and has mass, occupies space is called matter.
Composition of matter are:
- Jal
- Prithvi
- Agni (Tejas)
- Akash
- Vayu
Maharishi Kanada states that matter consists of kana means and.
We accept that, matter is consist of molecules.
2) State three properties of molecules of matter.
Answer:
Properties of matter-
- Matter is consist from tiny particles called molecules.
- Molecules have space between them.
- Molecules binds each other by a inter-molecular force.
3) What do you mean by inter-molecular spaces ? How do they vary in different states of matter ?
Answer: molecules have space between them. There is a space between any pair of molecules, this space is called inter-molecular space.
Inter-molecular space varies as-
Solid < liquid <gases.
4) What is meant by inter-molecular forces of attraction ? How do they vary in solids, liquids and gases ?
Answer: Each molecules attract another molecules in that matter by an attractive force, this force is called as inter-molecular force.
Solid > liquid > gases.
5) Which of the following are correct ?
(a) Solids have definite shape and definite volume.
(b) Liquids have definite volume but no definite shape.
(c) Gases have definite volume but no definite shape.
(d) Liquids have both definite shape and definite volume.
Answer: corrects statements are
(a) Solids have definite shape and definite volume.
(b) Liquids have definite volume but no definite shape.
6) Discuss the three states of matter : solid, liquid and gas on the basis of molecular model.
Answer: We can classify matter on the basis of molecular model in three types.
1) Solid
2) Liquid.
3) Gases.
1) Solid-
- Solids are rigid.
- They have definite volume and shape.
- Inter-molecular force is greater in solids than liquids and gases.
- Inter-molecular space is minimum in solids than liquids and gases.
- Molecules in solids vibrates with a kinetic energy but they do not leave their position.
2) Liquids-
- Liquids are not rigid.
- They have definite volume and not shape.
- Inter-molecular force is greater in liquids than gases but less than solids.
- Inter-molecular space is minimum in liquids than gases and maximum than solids.
- Molecules in liquids vibrates with a kinetic energy but they do not leave their boundaries.
3) Gases
- Gases are not also rigid.
- They do not have definite volume and shape.
- Inter-molecular force is minimum in gases than liquids and solids.
- Inter-molecular space is maximum in gases than liquids and solids.
- Molecules in solids vibrates with a greater kinetic energy and they can move anywhere.
7) What do you mean by ‘the change of state’ ? Write the flow chart showing the complete cycle of change of state.
Answer: Matter is classified on the basis of temperature in three categories.
- Solid
- Liquids
- Gases
These there states are interchangeable.
Solid, liquids and gases are interchangeable their state by absorbing or rejecting heat, this process is called as change of state.
8) Differentiate between melting point and boiling point. giving at least one example of each.
Answer:
Melting point-
Solids can be changes into liquid at fixed temperature, that temperature is called melting point.
Example- solid ice converts into liquid water at 0⁰ C therefore 0⁰ C is melting point of ice.
Boiling point-
Liquids can be changes into gases or vapour at fixed temperature, that temperature is called boiling point.
Example- liquid water converts into water vapour at 100⁰ C therefore 100⁰ C is boiling point of water.
9) Describe the process of condensation and sublimation with examples.
Answer:
Condensation- water vapour changes into solid by releasing heat at constant temperature, such process is called condensation. The atoms come closer to each other in condensation process.
Example- water steam converts into water by releasing heat at 100⁰ C.
Sublimation- we know that solid converts into liquid by absorbing heat and then it will converts into gases. But in some cases, solid will directly converts into gases. Such process are called as sublimation. Direct conversion from solid to gases takes place in sublimation process.
Example- Solid camphor converts into gases by absorbing heat.
10) Explain the terms melting and melting point.
Answer:
Melting- Melting is the process of conversion of solid into liquid.
Melting point-
Solids can be changes into liquid at fixed temperature, that temperature is called melting point.
Example- solid ice converts into liquid water at 0⁰ C therefore 0⁰ C is melting point of ice
11) Describe an experiment to demonstrate that a substance absorbs heat during melting without change in its temperature.
Answer: Melting is the process of transition from one state to another state when sufficient heat energy is given to it.
When some amount of heat energy is given to a solid it changes its state and get converted into liquid after reaching the particular temperature, this process is called as melting.
And the temperature at which solid starts to melt is called as melting point of that solid.
For example:
When we gave heat energy to wax which is solid it get melted totally after 55°C temperature rise in temperature. So we can say that the melting point of wax is 55°C.
But it is observed that the temperature of the solid remains constant till the total solid get melted completely. To study this we take an activity as discussed below.
We have taken a test tube in which some amount of wax is placed.
A tripod stand is taken over which a beaker filled with water is placed on the wire gauge as shown in figure below.
Now, we have clamped the test tube with vertical stand and it is inserted inside the water beaker.
Now, again we have clamped the thermometer such that it is inserted inside the test tube and it’s bottom bulb must deep inside the wax as shown in figure.
Now, we gave started giving heat to beaker with the help of burner and corresponding temperature of wax is noted after each minute.
*Observation table*
| Time (minute) | Temperature of wax
(⁰ C) |
| 0 | 25 |
| 1 | 30 |
| 2 | 35 |
| 3 | 40 |
| 4 | 45 |
| 5 | 50 |
| 6 | 55 |
| 7 | 55 |
| 8 | 55 |
We can observe from the observation table, that initially the temperature of the wax get increased and it becomes constant at 55°C then it will remain as it is.
And when total wax get melted completely then only the temperature starts rising again.
Hence, we can say that 55°C is the melting point of the wax and a solid absorbs heat during melting without change in its temperature is also proved.
12) Explain the terms vaporization and boiling point.
Answer:
Vaporization:
The conversation of liquid into gases at fixed temperature is called vaporization. Vaporization is Volant and rapid process.
Boiling point-
Liquids can be changes into gases or vapour at fixed temperature, that temperature is called boiling point.
13) A liquid can change into vapour state
(a) at a fixed temperature, and
(b) at all temperatures.
Name the processes involved in the two cases.
Answer: A liquid can change into vapour state at any temperature as well as fixed temperature.
The conversion of liquid into vapour at fixed temperature is carried out by vaporization process.
Vaporization:
The conversation of liquid into gases at fixed temperature is called vaporization. Vaporization is Volant and rapid process.
The conversion of liquid into vapour state at any temperature is carried out by evaporation process.
14) Some ice is taken in a beaker and its temperature is recorded after each one minute. The observations are listed below :
| Time (minute) | Temperature
(⁰ C) |
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 3.8 |
| 7 | 7.6 |
| 8 | 11.4 |
From the above observations what conclusion do you draw about the melting point of ice ?
Answer:
We draw some conclusions by studying above data. The temperature does not varies initially. All the molecules start to vibrating and rise temperature after 6 minutes. Therefore the melting point of ice will be 0⁰ C.
15) Describe an experiment to demonstrate that water absorbs heat during boiling at a constant temperature.
Answer: We know that water absorbs heat during boiling at a constant temperature. There is further change in temperature of the substance .
We can illustrate this with the help of an experiment.
- Take a beaker full of water.
- Insert thermometer in water to measure temperature.
- Heat it with the help of burner as shown in beaker.
- The assembly of the experiment is as shown in figure.
- Use watch to for recording time.
Observation table-
Observe time and temperature and note down.
| Time (minute) | Temperature (⁰ C) |
| 0 | 20 |
| 1 | 30 |
| 2 | 40 |
| 3 | 50 |
| 4 | 60 |
| 5 | 70 |
| 6 | 80 |
| 7 | 90 |
| 8 | 100 |
| 9 | 100 |
| 10 | 100 |
| 10 | 100 |
| 11 | 100 |
| 12 | 100 |
From above data we conclude that, temperature increases with time upto 100⁰ C. 100⁰ C is the boiling point of water. Once it reach at this temperature then there will not further increase in temperature.
16) State (a) the melting point of ice and (b) the boiling point of water.
Answer:
a) Melting point- Solids can be changes into liquid at fixed temperature, that temperature is called melting point.
The melting point of ice is 0⁰ C.
b) Liquids can be changes into gases or vapour at fixed temperature, that temperature is called boiling point.
The boiling point of water is 100⁰ C.
17) What is evaporation ?
Answer:
The process is of evaporation a vaporization is same. In both the cases liquid will convert into gases.. Evaporation takes place at any temperature but vapour takes place at fixed temperature.
Evaporation is slow and non violent process.
The process in which liquids will convert into gases at any temperature is called evaporation.
18) State three factors which affect the rate of evaporation of a liquid.
Answer:
The process in which liquids will convert into gases at any temperature is called evaporation.
Evaporation us depend on following factors-
- The area of substance- If the area of substance is greater then rate of evaporation is also greater.
- Temperature of the atmosphere- If the atmospheric temperature is greater then the rate of evaporation is also greater.
- Flow of air- Rate of evaporation varies directly with motion of air.
19) Wet clothes dry more quickly on a warm dry day than on a cold humid day. Explain.
Answer: wet clothes dry by the process of evaporation. We know that, rate of evaporation is depend on the atmospheric temperature. If the atmospheric temperature is greater then rate of evaporation is also greater. Therefore wet clothes dry more quickly on warm dry day than on a cold humid day.
20) Water in a dish evaporates faster than in a bottle. Give reason.
Answer: Water in a dish will converts into vapour by the process of evaporation. We know that rate of evaporation us depend on the area where the liquid exposed. The area of water in dish is greater than area water in bottle . Water in a dish evaporates faster than in bottle because of rate of evaporation is depend on area of exposure.
21) Why are volatile liquids such as alcohol and spirit stored in tightly closed bottles ?
Answer: The rate evaporation of volatile liquids such as alcohol and spirit is greater. If we did not store it in tightly bottle then they converts into vapour rabidly. We stored volatile liquids in tightly bottle to avoid evaporation.
22) A certain quantity of water is heated from 200C to 1000C. Its temperature is recorded after each 1 minute. The observations are :
| Time (minute) | Temperature (⁰ C) |
| 0 | 20 |
| 1 | 30 |
| 2 | 40 |
| 3 | 50 |
| 4 | 60 |
| 5 | 70 |
| 6 | 80 |
| 7 | 90 |
| 8 | 100 |
| 9 | 100 |
| 10 | 100 |
| 10 | 100 |
| 11 | 100 |
| 12 | 100 |
What conclusion do you draw from the above table about the boiling point of water ? Explain. Answer:
The temperature of water changes by rate of 10⁰/minute from 20⁰ C to 100⁰ C. After reaching 100⁰ C therefore is no further increase in temperature. Therefore we conclude that the boiling point of water is 100⁰ C.
23) Why is cooling produced on evaporation of a liquid ?
Answer: Evaporation occurs at any temperature. Heat is also required for the process of evaporation. This heat is supplied by atmospheric temperature. So the liquid absorb heat from surrounding and produces cooling effect.
24) Explain with an example that when a liquid evaporates, it takes heat from its surroundings.
Answer: Direct change of liquid into vapour at any temperature is called evaporation. Heat is absorbed from atmosphere in the process of evaporation because it produces cooling effect.
Example- Water becomes cold in earthen pot because of evaporation
25) Give two applications of evaporation.
Answer: Evaporation is slow process. It occurs at any temperature.
Applications of evaporation-
- We know that, evaporation produces cooling effects. Water stored in earthen pot get cooled.Water molecules around the earthen pot get evaporation and make water cooled.
- Our body maintains temperature in summer by releasingsweat. The sweat on our body get evaporation and produces cooling effect.
26) Explain why in hot summer days water remains cool in earthen pots.
Answer:
We know that, evaporation produces cooling effects. Water stored in earthen pot get cooled. Water molecules around the earthen pot get evaporation and make water cooled.
27) A patient suffering from high fever is advised to put wet cloth strips on his forehead. Why ?
Answer: Water gets evaporation at any temperature and produces cooling effects. We put wet cloth strips on forehead of the patient who suffer from high fever. The water in cloth strips get evaporation and helps to reduce the temperature of body by cooling effect.
28) What do you mean by sublimation ? Explain with an example.
Answer: The process in which solid is converted into gases directly by absorbing heat is called sublimation. Direct conversion of solid into gases takes place in the process of sublimation.
Sublimation process occurs as follows,
Example-
a) When we heat ammonium chloride, Camphor, naphthalene, iodine, and dry ice together then they directly produces their vapour.
b) The size of naphthalene balls decrease because of sublimation.
29) Why does the size of naphthalene balls decrease when left open ?
Answer: We know that, solids directly converts into liquid by sublimation process. The size of Naphthalene balls decreases because of sublimation process.
30) Describe an experiment to demonstrate the process of sublimation.
Answer:
We can illustrate the process of sublimation by an experiment ad follows.
- Put a powder of naphthalene and ammonium chloride in China dish.
- Put inverted funnelon China dish as shown in figure.
- Close the end of funnel by cotton.
- Put thus setup on wire mesh on stand.
- Heat the mixture by using burner as shown in figure.
Observations-
You can observe the vapour of ammonium chloride and Camphor on funnel. This is direct conversion of solid into gas. Such process is called sublimation.
