Class 8 ICSE
Selina solutions concise physics class 8 icse Solutions for Chapter 1 matter
Exercises in Chapter 1 matter Grade 8
Objective Questions
Short/Long Answer Questions
Questions in Objective Questions
Q1) Write true false for each statement
(a) The temperature of a substance remains unaffected during its change of state.
(b) Ice melts at 100°C.
(c) Water at 100°c has more heat than the steam by 100°C
(d) Evaporation of a liquid causes cooling.
(e) Water evaporates only at 100°C.
(f) Boiling takes place at all temperature.
(g) Evaporation takes place over the entire mass of the liquid.
(h) The process of a gas converting directly into solid is called vaporization.
(i) At high altitude water boils above 100°C.
(j) The melting point of ice is 0°C.
Ans :
Q1) True/False:
(a) False – The temperature of a substance changes during its change of state.
(b) False – Ice melts at 0°C, not 100°C.
(c) False – Water at 100°C has more heat than steam at 100°C.
(d) True – Evaporation of a liquid causes cooling.
(e) False – Water evaporates at all temperatures, not just at 100°C.
(f) False – Boiling takes place at a specific temperature for each substance, not at all temperatures.
(g) True – Evaporation takes place over the entire mass of the liquid.
(h) False – The process of a gas converting directly into a solid is called deposition, not vaporization.
(i) True – At high altitude, water boils above 100°C due to the decrease in atmospheric pressure.
(j) True – The melting point of ice is 0°C.
Q2) Fill in the blanks:
(a) Evaporation takes place at ____ temperatures.
(b) ________ is just the reverse of melting.
(c) _______ is a process that involves direct conversation 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) Intermolecular space is maximum in ______ less in _____ and the least in ______.
(h) Intermolecular force of attraction is maximum in ______, less in ______ and the least ______.
Ans : Fill in the blanks:
(a) Low (b) Freezing (c) Sublimation (d) Melting point (e) Atom (f) Motion, energy (g) Gases, liquids, solids (h) Solids, liquids, in gases
Q3) Match the columns:
| (a) Molecules | (i) water boils |
| (b) 100°C | (ii) evaporation |
| (c) 0°C | (iii) changes from solid to gas |
| (d) At all temperatures | (iv) matter |
| (e) Camphor | (v) water freezes |
Answer : Match the columns: (a) iv (b) i (c) v (d) ii (e) ii
Q4) Select the correct alternative:
(a) The inter-molecular force is maximum in
solids
gases
liquids
none of the above
(b) The inter-molecular space is maximum in
liquids
solids
gases
none of the above
(c) The molecules can move freely anywhere in
solids
gases
liquids
none of the above
(d) The molecules move only within the boundary of
liquids
solids
gases
none of the above
(e) The temperature at which a liquid gets converted into its vapour state is called its
melting point
boiling point
dewpoint
freezing point
(f) Rapid conversion of water into steam is an example of
evaporation
freezing
melting
vapourization
(g) Evaporation takes place from the
surface of liquid
throughout the liquid
mid-portion of the liquid
bottom of liquid
(h) Boiling takes place from the
the surface of the liquid
throughout the liquid
mid-portion of liquid
none of the above
Answers :
(a) Solids (b) Gases (c) Liquids (d) Liquids (e) Boiling point (f) Evaporation (g) Surface of liquid (h) Surface of liquid
4. Questions in Short/Long Answer Questions
Q1) Define the term matter. What is it composed of ?
Ans : Q1) Matter is anything that has mass and occupies space. It is composed of atoms, which are the smallest units of matter that retain the chemical properties of an element. Atoms are made up of a nucleus, which contains positively charged protons and neutral neutrons, and negatively charged electrons orbiting around the nucleus.
Q2) State three properties of molecules of a matter.
Ans :
Three properties of molecules of matter are:
- The molecules are very very small.
- The particles of matter have space between them
- The particles of matter are constantly moving
Q3) What do you mean by the inter- molecular spaces? How do they vary in different states of matter?
Ans : Intermolecular spaces are the spaces between molecules in a substance. They vary in different states of matter. In a solid, the molecules are tightly packed together, so the intermolecular spaces are very small. In a liquid, the molecules are less tightly packed, so the intermolecular spaces are larger than in a solid. In a gas, the molecules are far apart from each other, so the intermolecular spaces are very large.
Q4) What is meant by the intermolecular forces of attraction?
Intermolecular forces of attraction are the attractive forces between molecules in a substance. They are responsible for holding the molecules together in a substance. These forces can be weak or strong depending on the type of molecule and the conditions of the environment.
Q5) Which of the following are correct?
(a) Solids have definite shape and definite volume.
(b) Liquid have definite volume but do not have definite shape.
(c) Gases have definite volume but no definite shape.
(d) Liquids have definite shape and definite volume.
Ans : (a) True (b) True (c) False (d) False
Q6) Discuss the three states of matter solid,liquids and gas on the basis of molecular model.
Answer :
Solids – Molecules are tightly packed together and have very little movement. They have a definite shape and volume.
Liquids – Molecules are more spread out and can move around each other. They have a definite volume, but no definite shape.
Gases – Molecules are widely spread out and move freely. They have no definite shape or volume.
Q7) What do you mean by the change of state? Write the flowchart showing the complete cycle of change of state.
Ans : Change of state refers to the physical transformation of a substance from one state to another. The complete cycle of change of state is shown in the flowchart below: Solid → Melting → Liquid → Evaporation → Gas
Q8) Differentiate between melting point and boiling point, giving at least one example of each.
Ans : elting point is the temperature at which a solid melts to become a liquid, while boiling point is the temperature at which a liquid boils to become a gas. An example of melting is the melting of ice to form water, and an example of boiling is the boiling of water to form steam.
Q9) Describe the process of condensation and sublimation with examples.
Ans : Condensation is the process by which a gas changes into a liquid on cooling, while sublimation is the process by which a solid changes directly into a gas on heating, without passing through the liquid state. Examples of condensation include the formation of dew on grass in the morning, and the formation of clouds in the sky. An example of sublimation is the conversion of dry ice (solid carbon dioxide) to gas.
Q10) Explain the term melting and melting point.
Ans : Melting is the process by which a solid is heated to its melting point and changes into a liquid. The melting point is the temperature at which a solid melts to become a liquid.
Q11) Describe an experiment to demonstrate that a substance absorbs heat during melting without change in its temperature.
Ans : To demonstrate that a substance absorbs heat during melting without change in its temperature, take a beaker of ice and note its initial temperature. Place the beaker on a heat source and keep stirring the ice until it completely melts. Record the final temperature of the water. It will be observed that the temperature of the ice remains constant during melting, but the ice absorbs heat from the surroundings to melt.
Q12) Explain the terms vaporization and boiling point.
Ans : Vaporization refers to the process in which a liquid changes into a gas or vapor. It can occur either through evaporation (slow process at the surface of the liquid) or boiling (rapid process throughout the liquid). Boiling point refers to the temperature at which a liquid boils and turns into a vapor at a given pressure.
Q13) A liquid can change into vapours state
(a) At a fixed temperature, and
(b) At all temperatures
Name the process involved in two cases.
Ans :
(a) The process involved in this case is boiling. At a fixed temperature, the liquid continues to receive heat until the boiling point is reached, and then it starts boiling and changes into the vapour state.
(b) The process involved in this case is evaporation. At all temperatures, the liquid molecules at the surface gain enough energy to break the intermolecular forces and escape into the air, thus changing into the vapour state.
Q14) Some ice is taken in temperature is recorded after each one minute. The observations are listed below:
| Time (in minute) | Temperature (in °C) |
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 3.8 |
| 7 | 7.6 |
| 8 | 11.4 |
Ans : From the above observations what conclusion do you draw about the melting point of ice ?
The temperature remains constant at 0°C until all the ice has melted. This indicates that the melting point of ice is 0°C.
Q15) Describe an experiment to demonstrate that water absorbs heat during boiling at a constant temperature.
Ans : Take a beaker and fill it with water. Place a thermometer in the water and heat the beaker on a hot plate. Once the water starts boiling and the thermometer reaches a constant temperature, place an ice cube on top of the water. Observe the temperature on the thermometer, which should decrease due to the absorption of heat by the ice cube during its melting process.
Q16) State (a) the melting point of ice, and (b) the boiling point of water.
Ans : a) The melting point of ice is 0°C. (b) The boiling point of water is 100°C.
Q17) What is evaporation?
Ans : Evaporation refers to the process in which a liquid changes into a gas or vapor at a temperature below its boiling point.
Q18) State three factors which affect the rate of evaporation of a liquid.
Ans :
Three factors that affect the rate of evaporation are:
- Temperature: Higher temperature results in more kinetic energy and thus faster movement of molecules at the surface, which increases the rate of evaporation.
- Surface area: Larger surface area provides more space for molecules to escape from the surface, thus increasing the rate of evaporation.
- Humidity: Higher humidity means more moisture in the air, which reduces the concentration gradient between the liquid and the air, thereby slowing down the rate of evaporation.
Q19) Wet clothes dry more quickly on a warm day than on a cold humid day. Explain.
Ans : Â Wet clothes dry more quickly on a warm day than on a cold humid day because a warm day has lower relative humidity, which creates a greater concentration gradient between the wet clothes and the air. This increases the rate of evaporation, resulting in faster drying.
Q20) Water in a dish evaporates faster than in a bottle. Give reason
Ans : Water in a dish evaporates faster than in a bottle because a dish has a larger surface area, which provides more space for the water molecules to escape from the surface, thus increasing the rate of evaporation.
Q21) Why are volatile liquids such as alcohol and spirit stored in tightly closed bottles?
Ans : Volatile liquids such as alcohol and spirit are stored in tightly closed bottles to prevent evaporation, which can lead to loss of volume and concentration.
Q22) A certain quantity of water is heated from 20°C TO 100°C. Its temperature is recorded after 1 minutes each. The observations are
| Time (in minute) | Temperature (in °C) |
| 0 | 20 |
| 1 | 30 |
| 2 | 40 |
| 3 | 50 |
| 4 | 60 |
| 5 | 70 |
| 6 | 80 |
| 7 | 90 |
| 8 | 100 |
| 9 | 100 |
| 10 | 100 |
| 11 | 100 |
| 12 | 100 |
What conclusion do you draw from the above table about the boiling point of water? Explain.
Ans : The boiling point of water is 100°C. At this temperature, the water starts boiling and remains at the same temperature until all of it has turned into steam.
Q23) Why is cooling produced on evaporation of a liquid?
Ans : Cooling is produced on evaporation of a liquid because when a liquid evaporates, the molecules with the highest kinetic energy escape from the surface, leaving behind molecules with lower kinetic energy. This reduces the average kinetic energy and thus the temperature of the remaining liquid.
Q24) Explain with an example to demonstrate that when a liquid evaporates, it takes heat from its surroundings.
Ans : When a liquid evaporates, it takes heat from its surroundings because the process of evaporation requires energy to overcome the intermolecular forces holding the liquid together. This energy is obtained from the surroundings in the form of heat. For example, when sweat evaporates from our skin, it takes heat from the body, resulting in cooling.
Q25) Give two applications of evaporation.
Ans :
Two applications of evaporation are:
- Cooling effect: Evaporation is used for cooling purposes, such as in air conditioners, refrigerators, and cooling towers. Water is evaporated in these systems to remove heat from the surroundings, thus cooling the air or liquid.
- Separation of substances: Evaporation is used for separating a mixture of liquids or solids. For example, saltwater can be separated into salt and water by evaporating the water and leaving the salt behind.
Q26) Explain why on hot summer days water remains cool in earthen pots.
Ans : Water remains cool in earthen pots on hot summer days due to the process of evaporation. The porous surface of the earthen pot allows water to seep through and evaporate on the surface. This process of evaporation removes heat from the water and keeps it cool.
Q27) A patient suffering from high fever is advised to put wet cloth strips on his forehead. Why?
Ans : A patient suffering from high fever is advised to put wet cloth strips on his forehead to bring down their body temperature. The wet cloth strips cool down the forehead by evaporation. As the water evaporates from the cloth, it absorbs heat from the body, and the evaporation process cools down the body temperature.
Q28) What do you mean by sublimation? Explain with an example
Ans : Sublimation is the process by which a solid directly changes into a gas without passing through the liquid state. For example, when solid iodine is heated, it directly changes into a gas without melting into a liquid. The reverse process, where a gas changes directly into a solid without passing through the liquid state, is called deposition.
Q29) Why does the size of naphthalene balls decrease when left open?
Ans Naphthalene balls decrease in size when left open due to the process of sublimation. Naphthalene balls are a solid form of mothballs made of naphthalene, which readily sublimes at room temperature. When the balls are left open, the naphthalene sublimes, and the size of the ball decreases.
Q30) Describe an experiment to demonstrate the process of sublimation.
Ans :
An experiment to demonstrate the process of sublimation can be performed using iodine crystals. The steps of the experiment are:
- Take a few crystals of iodine in a test tube and cover it with a small piece of filter paper.
- Heat the test tube gently with a Bunsen burner.
- Observe the iodine crystals. As they are heated, they will turn into a purple vapor that will sublimate and condense on the filter paper.
- Remove the heat source and observe the sublimated iodine on the filter paper.
This experiment demonstrates how the solid iodine changes directly into a gas without passing through the liquid state, i.e., sublimation.