Chapter 1: Matter in Our Surroundings
This study material is aligned with the KVS Class IX Science Student Support Material (2025-26). It provides key concepts, explanations, and a full question bank for thorough preparation.
1. Definition of Matter
Matter is a substance which occupies space and has mass.
Air, Earth, Fire, Sky and water are five basic elements, known as the 'Panch Tatwa'. According to the earlier Indian Philosophers, everything—whether living or non-living—is made up of these five elements.
2. Characteristics of Particles of Matter
i) Matter is made up of particles
Matter is not continuous but particulate in nature. Particles of one type of matter get into the spaces between particles of the other. This shows that there is enough space between particles of matter.
Example: The particles of sugar and salt get evenly distributed in water when dissolved.
ii) Particles of matter are very small in size beyond our imagination
The particles of matter are extremely small, far beyond our imagination. For instance, even a tiny crystal of potassium permanganate contains millions of small particles that can color a massive volume of water.
iii) Particles of matter have space between them
The space between particles is known as interparticle space or intermolecular space. Because of these spaces, we can easily dissolve one form of matter into another.
iv) Particles of matter are continuously moving
Moving particles possess kinetic energy. Particles move faster when the temperature rises because, with an increase in temperature, the kinetic energy of the particles increases. Particles of solids have very less kinetic energy while gaseous particles have extremely high kinetic energy.
Kinetic Energy: The energy possessed by a moving object is called kinetic energy.
Diffusion: The process of flow of matter from a region of high concentration to a region of low concentration is called diffusion. On heating, the diffusion becomes faster because the kinetic energy of particles increases, accelerating their random movement and intermixing.
v) Particles of matter attract each other
The particles of matter have an attractive force acting between them which keeps them together. Particles of solid have the highest attraction force, causing these particles to remain very close to each other.
3. Three States of Matter
Based on physical properties, matter exists in three states: Solid, Liquid, and Gas.
| Property | Solid State | Liquid State | Gaseous State |
|---|---|---|---|
| Nature | Hard & rigid | Fluid | Very fluid |
| Shape & Volume | Definite shape & volume | Indefinite shape but definite volume | Both are indefinite |
| Density | High | Less than solid but greater than gaseous | Very less density |
| Intermolecular Space | Very small | Intermediate of solid and gas | Very large |
| Intermolecular Force | Very strong | Weak | Very weak |
| Compressibility | Negligible | Very small | Highly compressible |
| Kinetic Energy | Low | High than solid | Very high |
| Diffusion | Negligible | Slow | Very fast |
4. Effect of Change in Temperature
The state of matter can be changed into another state by changing the temperature. A solid can change into liquid while a liquid can change into vapour upon heating:
Melting Point
The temperature at which a solid melts and becomes a liquid at atmospheric pressure is called its melting point. For example, the melting point of ice is $0^{\circ}\mathrm{C}$ ($273\mathrm{~K}$).
Fusion
The process in which a solid state changes into a liquid state by melting is known as fusion.
The Latent Heat of Fusion
The amount of heat energy required to change $1\mathrm{~kg}$ of solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion.
Boiling Point
The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point. It is a bulk phenomenon. For example, the boiling point of water is $100^{\circ}\mathrm{C}$ ($373\mathrm{~K}$).
The Latent Heat of Vaporisation
The amount of heat energy that is required to change $1\mathrm{~kg}$ of liquid into vapour at atmospheric pressure at its boiling point is known as the latent heat of vaporisation.
Sublimation
The change of solid directly into the gaseous state without passing through the liquid state upon heating is called sublimation. Examples: Iodine, Ammonium chloride, camphor, naphthalene, solid $\mathrm{CO_2}$, etc.
Deposition
The change of gas directly into the solid state without passing through the liquid state upon cooling is called deposition.
5. Conversion of Temperature
(a) Conversion of Celsius scale $(^{\circ}\mathrm{C})$ into Kelvin scale $(\mathrm{K})$
To convert temperature on the Celsius scale to the Kelvin scale, add $273$ to the Celsius value.
- $0^{\circ}\mathrm{C} + 273 = 273\mathrm{~K}$
- $25^{\circ}\mathrm{C} + 273 = 298\mathrm{~K}$
(b) Conversion of Kelvin scale $(\mathrm{K})$ into Celsius scale $(^{\circ}\mathrm{C})$
To convert temperature on the Kelvin scale to the Celsius scale, subtract $273$ from the Kelvin value.
- $300\mathrm{~K} - 273 = 27^{\circ}\mathrm{C}$
- $393\mathrm{~K} - 273 = 120^{\circ}\mathrm{C}$
Comparison between Fusion and Vaporisation
| Fusion | Vaporisation |
|---|---|
| Fusion is the process of melting, in which solid turns into its liquid state. | Vaporisation is the process of conversion of a liquid state into vapour state. |
| The required heat for fusion is known as latent heat of fusion. | The required heat for vaporisation is known as latent heat of vaporisation. |
| It is an effect of temperature. | It is also an effect of temperature. |
| Example: Conversion of ice into water. | Example: Conversion of water into water vapour. |
6. Effects of Change of Pressure
A gas can liquefy by increasing pressure and decreasing temperature. By this process, the particles of gas get compressed and the space between particles becomes less. As a result, the gaseous state changes into liquid state.
Solid carbon dioxide is also known as dry ice. Solid $\mathrm{CO_2}$ looks like ice but does not wet a piece of paper or glass. If the pressure on solid carbon dioxide is reduced nearly to one atmosphere, it directly changes to the vapour state without passing through the liquid state.
7. Evaporation
The phenomenon of change of liquid to the vapour state at any temperature below the boiling point of the liquid is called evaporation. Evaporation is a surface phenomenon.
Factors affecting the rate of evaporation:
- Increase of surface area: Evaporation is a surface phenomenon; increasing surface area increases the rate of evaporation.
- Increase of temperature: Increasing temperature increases the kinetic energy of particles, making them escape more easily.
- Increase in wind speed: Stronger winds move the vapour particles away rapidly, increasing the rate of evaporation.
- Decrease in humidity: Humidity is the amount of water vapour present in the air. If humidity is low, the rate of evaporation increases.
Difference between Boiling and Evaporation
| Boiling | Evaporation |
|---|---|
| Boiling occurs only when a liquid is heated on its boiling point. | Evaporation of a liquid occurs naturally. |
| It happens at a specific temperature. | It takes place at all temperatures. |
| No physical conditions affect the boiling process. | It is affected by temperature, surface area, wind speed, and humidity etc. |
| It does not cause cooling on the surface. | It causes cooling during evaporation. |
| It is a bulk phenomenon. | It is a surface phenomenon. |
8. Everyday Phenomena of Evaporation Cooling
When water changes into vapour, it loses its energy. It regains energy from the surroundings. This process makes the surroundings cool.
a) When you pour some acetone on your palm?
Ans: The particles of acetone gain energy from your palm and surroundings and evaporate. This loss of heat energy makes the palm feel cool.
b) When water sprinkles on a hot surface during summer?
Ans: Water absorbs heat energy from the hot surface to undergo vaporisation, thereby lowering the temperature of the surface and causing a cooling effect.
c) When a cold-drink bottle is kept in the open?
Ans: Water vapour present in the air comes in contact with the cold outer surface of the bottle, loses its energy, and condenses into visible liquid water droplets.
d) If we wear white or cotton clothes in summer?
Ans: Cotton is an excellent absorber of water. It absorbs sweat from our body and exposes it to the surface for rapid evaporation, making our body feel comfortable and cool.
9. Chapterwise Question Bank
Multiple Choice Questions (1 Mark Each)
MCQ 1 A student observes that a substance changes from solid to liquid at a certain temperature. What can be inferred about the substance?
(a) It has a high melting point (b) It has a low melting point
(c) It is a pure substance (d) It is a mixture.
MCQ 2 A student is given a substance that sublimes easily. What can be done to prevent it from subliming?
(a) Increase the temperature (b) Decrease the temperature
(c) Increase the pressure (d) Decrease the pressure
MCQ 3 What will happen if we increase temperature of the particles of a substance?
(a) Particles come close together (b) Particles move slower
(c) Particles move faster (d) Particles remain stationary
MCQ 4 Severe burns will be produced by which of the following?
(a) cold water (b) hot water (c) boiling water (d) steam
MCQ 5 During summer, water kept in an earthen pot becomes cool due to the phenomenon of:
(a) Diffusion (b) Transpiration (c) Distillation (d) Evaporation
MCQ 6 The most favourable conditions for converting gas into liquid are:
(a) High pressure, low temperature (b) Low pressure, low temperature
(c) Low pressure, high temperature (d) High pressure, high temperature
Assertion-Reason Based Questions (1 Mark Each)
Directions: Choose (a) if both A and R are true and R is correct explanation of A; (b) if both A and R are true but R is not the correct explanation; (c) if A is true but R is false; (d) if A is false but R is true.
A/R 7
Assertion (A): Air is a mixture.
Reason (R): Air consists of various gaseous compounds and particulate matters.
A/R 8
Assertion (A): Sublimation is the process of conversion of a solid to a gas.
Reason (R): Sublimation occurs when the particles of a substance gain enough energy to overcome the intermolecular forces.
A/R 9
Assertion (A): Liquids take the shape of their container.
Reason (R): The particles of a liquid are free to move and have no fixed position.
A/R 10
Assertion (A): Wet clothes do not dry in dark.
Reason (R): Evaporation also occurs in the dark.
Very Short Answer Questions (2 Marks Each)
Q11 Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Why?
Q12 During inter-conversion of states of matter the temperature remains constant. Explain.
Q13 (a) Gases are compressible but not liquids. Justify?
(b) The property of gases helps aquatic plants and animals to survive in water. How is it possible?
Q14 The gases exert more pressure on the walls of the container than the solids. Identify the reason?
Q15 We see water droplets on the outer surface of a glass containing ice cold water. From where does this water come?
Short Answer Questions (3 Marks Each)
Q16 (a) Identify the different states of matter based on molecular arrangement.
(b) Compare the different states of matter on the basis of intermolecular force of attraction and intermolecular space.
Q17 Amit perspires a lot on a hot humid day. Explain the reason.
Q18 It is advisable to use a pressure cooker at higher altitudes. Suggest the reason.
Q19 The high compressibility property of gas is useful to us. Explain with real-life examples.
Long Answer Questions (5 Marks Each)
Q20 Explain giving examples the various factors on which rate of evaporation depends.
Q21 (a) How do solids, liquids and gases exhibit the properties of: (i) Rigidity, (ii) Diffusion, and (iii) Compressibility?
(b) Arrange them in ascending order of magnitude for each property.
Case Study Based Questions (4 Marks Each)
Case Study 22 A matter is anything that has mass and occupies space. Pen, paper, clips, sand, air, ice, etc. are different forms of matter. Every matter is made up of small particles. These particles are so tiny that they can't be seen with naked eyes. Let's see about the different characteristics of particles of matter.
Questions:
i) Which of the following is not matter?
(a) Pen (b) air (c) smell of perfume (d) None of these
ii) Thoughts coming in our mind are examples of matter. True or false?
(a) True (b) False (c) None of these (d) both True and False
iii) Enlist any two properties of particles of matter.
Case Study 23 Do we always need to heat or change pressure for changing the state of matter? Can you quote some examples from everyday life where change of state from liquid to vapour takes place without the liquid reaching the boiling point? In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapour. This phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.
Questions:
i) Evaporation of liquid takes place at:
(a) Boiling point (b) Above boiling point (c) Below boiling point (d) None of these
ii) Evaporation takes place at surface of liquid because:
(a) They are heavy compared to other particles (b) They have sufficient kinetic energy to break the force of attraction (c) They are lightweight compared to other particles (d) None of these
iii) Distinguish between evaporation and boiling (write two points).
No comments:
Post a Comment