Class 9 Science Notes Chapter 1 (Matter in Our Surroundings) – Science Book

Alright class, let's focus on Chapter 1: 'Matter in Our Surroundings'. This is a fundamental chapter, and understanding these concepts well is crucial, not just for your class exams but also for various government competitive exams where basic science is often tested. Pay close attention.

Chapter 1: Matter in Our Surroundings - Detailed Notes for Competitive Exams

1. What is Matter?

• Definition: Anything that occupies space (has volume) and has mass is called matter.
• Examples: Air, water, stones, clouds, plants, animals, even a tiny grain of sand or a drop of water.
• Early Indian Philosophy: Classified matter into five basic elements – ‘Panch Tatva’ – Air, Earth, Fire, Sky, and Water. Modern scientists classify matter based on physical and chemical properties.
• Particle Nature of Matter:
  • Matter is made up of extremely small particles (atoms or molecules).
  • These particles are too small to be seen with the naked eye.

2. Characteristics of Particles of Matter:

• (a) Particles of matter have space between them: This is evident when substances like sugar, salt, Dettol, or potassium permanganate dissolve in water. The particles of the solute get into the spaces between the particles of the solvent (water).
• (b) Particles of matter are continuously moving:
  • They possess kinetic energy.
  • As temperature increases, kinetic energy increases, and particles move faster.
  • This movement is responsible for phenomena like diffusion (intermixing of particles of different types of matter on their own) and Brownian motion (random movement of particles suspended in a fluid).
  • Diffusion is fastest in gases, slower in liquids, and negligible in solids. Rate of diffusion increases with temperature.
• (c) Particles of matter attract each other:
  • This force of attraction holds the particles together.
  • The strength of this force varies from one kind of matter to another.
  • It is strongest in solids, intermediate in liquids, and weakest (almost negligible) in gases. This force is known as the intermolecular force of attraction.

3. States of Matter:
Matter primarily exists in three states: Solid, Liquid, and Gas.

• (a) The Solid State:

  • Properties: Definite shape, distinct boundaries, fixed volume, negligible compressibility, rigid.
  • Particle Arrangement: Particles are tightly packed with very strong intermolecular forces and minimal intermolecular spaces. Particles vibrate about their mean positions but do not move freely.
  • Examples: Stone, wood, iron, ice, sugar, salt.
  • Exceptions: Rubber band (changes shape under force, regains shape), Sponge (has minute holes with trapped air, compressible). Sugar/salt take the shape of the container but individual crystals retain their shape.

• (b) The Liquid State:

  • Properties: No fixed shape (take the shape of the container), fixed volume, low compressibility, fluid (can flow).
  • Particle Arrangement: Particles are less tightly packed than solids, with weaker intermolecular forces and larger intermolecular spaces. Particles can slide over one another.
  • Examples: Water, milk, oil, juice, alcohol.
  • Diffusion: Solids, liquids, and gases can diffuse into liquids. Gases (like Oxygen and Carbon Dioxide) dissolve in water, essential for aquatic life. Rate of diffusion in liquids is higher than in solids.

• (c) The Gaseous State:

  • Properties: No fixed shape, no fixed volume (take the shape and volume of the container), highly compressible, fluid (can flow easily).
  • Particle Arrangement: Particles are far apart with negligible intermolecular forces and large intermolecular spaces. Particles move randomly at high speeds.
  • Pressure: Gas particles collide with each other and the walls of the container, exerting pressure.
  • Examples: Air, oxygen, nitrogen, hydrogen, LPG (Liquefied Petroleum Gas), CNG (Compressed Natural Gas).
  • Diffusion: Gases diffuse very rapidly due to high speed of particles and large spaces. This allows smells (perfume, hot food) to travel quickly.

Comparison of Solid, Liquid, and Gas:

4. Can Matter Change Its State?
Yes, matter can change from one state to another by changing temperature or pressure.

• (a) Effect of Change of Temperature:

  • Melting (Fusion): Solid → Liquid. The process occurs at a specific temperature called the Melting Point. The melting point of ice is 0°C (273.15 K). During melting, the temperature remains constant until all the solid melts.
  • Latent Heat of Fusion: The amount of heat energy required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point. (Latent means 'hidden' - the heat supplied doesn't raise the temperature). For ice, it's 3.34 x 10⁵ J/kg. Particles in water at 0°C have more energy than particles in ice at the same temperature.
  • Boiling (Vaporization): Liquid → Gas. The process occurs at a specific temperature called the Boiling Point. The boiling point of water is 100°C (373.15 K). Boiling is a bulk phenomenon (particles from the entire bulk of the liquid gain enough energy to change into vapour).
  • Latent Heat of Vaporization: The amount of heat energy required to change 1 kg of a liquid into gas at atmospheric pressure at its boiling point. For water, it's 22.6 x 10⁵ J/kg. Particles in steam at 100°C have more energy than particles in water at the same temperature. This is why steam causes more severe burns than boiling water.
  • Condensation: Gas → Liquid. Occurs on cooling.
  • Freezing (Solidification): Liquid → Solid. Occurs on cooling at the Freezing Point (which is the same as the melting point for a pure substance).
  • Sublimation: Solid → Gas (directly, without passing through the liquid state). Examples: Camphor, Ammonium chloride, Naphthalene balls, Iodine, Dry Ice (Solid CO₂).
  • Deposition: Gas → Solid (directly). Example: Frost formation.

• (b) Effect of Change of Pressure:

  • Increasing pressure and decreasing temperature can liquefy gases. Applying pressure brings gas particles closer, increasing intermolecular forces. Reducing temperature lowers kinetic energy.
  • Example: LPG cylinders contain petroleum gas liquefied under pressure.
  • Dry Ice: Solid Carbon Dioxide (CO₂) gets converted directly to gaseous state on decrease of pressure to 1 atmosphere without coming into the liquid state. High pressure is used to keep CO₂ in solid form.

Interconversion of the Three States of Matter:

graph TD
    A[Solid] -- Melting/Fusion --> B(Liquid);
    B -- Freezing/Solidification --> A;
    B -- Boiling/Vaporization --> C(Gas);
    C -- Condensation/Liquefaction --> B;
    A -- Sublimation --> C;
    C -- Deposition --> A;

5. Evaporation:

• Definition: The phenomenon of change of a liquid into vapours at any temperature below its boiling point.
• It is a surface phenomenon. Particles at the surface gain enough energy to overcome the forces of attraction and escape into the vapour phase.
• Factors Affecting Evaporation:
  • (i) Surface Area: Increases with an increase in surface area (e.g., spreading clothes to dry).
  • (ii) Temperature: Increases with an increase in temperature (more particles get enough kinetic energy).
  • (iii) Humidity: Decreases with an increase in humidity (humidity is the amount of water vapour in the air; if the air is already saturated, it can't hold more).
  • (iv) Wind Speed: Increases with an increase in wind speed (wind carries away water vapour particles, allowing more evaporation).
• Evaporation Causes Cooling:
  • During evaporation, particles of the liquid absorb energy (latent heat of vaporization) from the surroundings to change into vapour. This absorption of energy makes the surroundings cool.
  • Examples: Feeling cool after sweating, cooling of water in an earthen pot (matka), putting acetone/spirit on palm feels cool, wearing cotton clothes in summer (cotton absorbs sweat and exposes it to the atmosphere for easy evaporation).

6. Other States of Matter (Brief Mention for Competitive Exams):

• Plasma: A state consisting of super energetic and super excited particles in the form of ionized gases. Found in fluorescent tubes (contain Helium or Neon gas), neon sign bulbs, stars, and the sun. Created at very high temperatures.
• Bose-Einstein Condensate (BEC): A state formed by cooling a gas of extremely low density to super-low temperatures. Predicted by Albert Einstein based on calculations by Satyendra Nath Bose.

7. Units:

• Temperature:
  • SI unit: Kelvin (K)
  • Common unit: Degree Celsius (°C)
  • Conversion: K = °C + 273.15 (often approximated as K = °C + 273 for calculations)
  • 0°C = 273.15 K
  • 100°C = 373.15 K
• Pressure:
  • SI unit: Pascal (Pa)
  • Common unit: Atmosphere (atm)
  • 1 atmosphere (atm) = 1.01 x 10⁵ Pa
  • Atmospheric pressure at sea level is 1 atm.

Multiple Choice Questions (MCQs):

1. Which of the following phenomena increases on increasing the temperature?
   (a) Diffusion
   (b) Evaporation
   (c) Compression of gases
   (d) Both (a) and (b)

2. Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identify the correct set of conditions.
   (a) Low temperature, low pressure
   (b) High temperature, low pressure
   (c) Low temperature, high pressure
   (d) High temperature, high pressure

3. The property of flow is unique to fluids. Which one of the following statements is correct?
   (a) Only gases behave like fluids
   (b) Gases and solids behave like fluids
   (c) Gases and liquids behave like fluids
   (d) Only liquids are fluids

4. During summer, water kept in an earthen pot becomes cool because of the phenomenon of:
   (a) Diffusion
   (b) Transpiration
   (c) Osmosis
   (d) Evaporation

5. Which condition out of the following will increase the evaporation of water?
   (a) Increase in temperature of water
   (b) Decrease in temperature of water
   (c) Less exposed surface area of water
   (d) Adding common salt to water

6. What is the term used to describe the phase change of a solid directly into a gas?
   (a) Evaporation
   (b) Condensation
   (c) Sublimation
   (d) Fusion

7. Which of the following has the strongest inter-particle forces at room temperature?
   (a) Oxygen
   (b) Water
   (c) Bromine
   (d) Iron

8. Convert the temperature of 373°C to the Kelvin scale.
   (a) 646 K
   (b) 100 K
   (c) 373 K
   (d) 546 K

9. Dry ice is:
   (a) Water in solid state
   (b) Water in gaseous state
   (c) CO₂ in liquid state
   (d) CO₂ in solid state

10. Why does the temperature remain constant during the boiling of water even though heat is continuously supplied?
    (a) Heat supplied is lost to the surroundings.
    (b) Water has high specific heat capacity.
    (c) Heat supplied is used up to overcome the forces of attraction between water particles (latent heat of vaporization).
    (d) The thermometer is faulty.

Answer Key for MCQs:

1. (d)
2. (c)
3. (c)
4. (d)
5. (a)
6. (c)
7. (d)
8. (a) [Calculation: K = °C + 273 = 373 + 273 = 646 K]
9. (d)
10. (c)

Revise these notes thoroughly. Remember the definitions, the differences between the states of matter, the factors affecting state changes and evaporation, and the associated terminology like latent heat and sublimation. Good luck with your preparation!