Class 9 Science Notes Chapter 1 (Chapter 1) – Examplar Problem (English) Book

Alright students, let's get straight into Chapter 1: Matter in Our Surroundings from your NCERT Exemplar. This chapter forms the foundation for understanding chemistry, and questions frequently appear in various government exams. Pay close attention to the details.

Chapter 1: Matter in Our Surroundings - Detailed Notes for Exam Preparation

1. Definition of Matter:

• Anything that occupies space (has volume) and has mass is called matter.
• Examples: Air, water, sugar, sand, stars, planets, a drop of water, a grain of sand – everything in this universe is made up of material which scientists have named "matter".
• Things like friendship, love, hate, smell, taste, thought are not matter as they don't occupy space or have mass. (Note: The smell itself isn't matter, but the gaseous particles carrying the smell are).

2. Physical Nature of Matter:

• Matter is made up of particles: This was proven by experiments like dissolving salt/sugar in water without a significant change in volume, indicating particles fit into the spaces between water particles.
• These particles are very small: Demonstrated by the dilution experiment with potassium permanganate (KMnO₄) or Dettol, where the colour/smell persists even after multiple dilutions, showing a small amount of substance contains millions of tiny particles.

3. Characteristics of Particles of Matter:

• (a) Particles of matter have space between them: This is evident when sugar, salt, Dettol, or KMnO₄ dissolve in water; their particles get distributed in the spaces between the water particles. The extent of space varies between states of matter (least in solids, most in gases).
• (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 diffusion: the intermixing of particles of two different types of matter on their own.
  • Diffusion is fastest in gases, slower in liquids, and very slow (almost negligible) in solids.
  • Rate of diffusion increases with temperature. (Example: Smell of hot food reaches faster than cold food).
• (c) Particles of matter attract each other:
  • There exists a force of attraction between the particles, holding them together.
  • The strength of this force varies from one kind of matter to another.
  • This force is strongest in solids, intermediate in liquids, and weakest in gases.

4. States of Matter:
Based on the variation in the characteristics of particles (space, kinetic energy, force of attraction), matter exists mainly in three states:

• (a) The Solid State:

  • Definite shape and distinct boundaries.
  • Fixed volume.
  • Negligible compressibility.
  • Rigid.
  • Particles are tightly packed with minimum space between them.
  • High forces of attraction between particles.
  • Minimum kinetic energy of particles (they vibrate about their mean positions).
  • Examples: Stone, wood, iron, sugar, salt.
  • Exceptions/Notes: Rubber band changes shape under force but regains it (solid). Sugar/salt take the shape of the container but individual crystal shape is fixed (solid). Sponge has pores filled with air; it's compressible due to expulsion of air, but the material itself is solid.

• (b) The Liquid State:

  • No fixed shape; take the shape of the container.
  • Fixed volume.
  • Can flow (fluidity).
  • Low compressibility (more than solids, much less than gases).
  • Particles are less tightly packed than solids, with more space between them.
  • Weaker forces of attraction than solids.
  • Higher kinetic energy than solids; particles can slide over one another.
  • Diffusion rate is higher than solids.
  • Examples: Water, milk, oil, juice.
  • Note: Gases like oxygen and carbon dioxide can diffuse and dissolve in water, essential for aquatic life.

• (c) The Gaseous State:

  • No fixed shape or volume; take the shape and volume of the container.
  • Highly compressible.
  • Fluid (can flow easily).
  • Particles are far apart with large spaces between them.
  • Negligible forces of attraction between particles.
  • Highest kinetic energy; particles move randomly at high speeds.
  • Exert pressure on the walls of the container due to collisions of particles with the walls.
  • Highest rate of diffusion.
  • Examples: Air, oxygen, hydrogen, nitrogen, LPG (Liquefied Petroleum Gas), CNG (Compressed Natural Gas).

5. Other States of Matter (Mentioned for completeness):

• Plasma: Super-energetic and super-excited particles in the form of ionised gases. Found in fluorescent tubes, neon sign bulbs, stars (including the Sun). Created at very high temperatures.
• Bose-Einstein Condensate (BEC): Formed by cooling a gas of extremely low density to super-low temperatures. Predicted by Satyendra Nath Bose and Albert Einstein.

6. Can Matter Change Its State?
Yes, by changing temperature or pressure.

• (a) Effect of Change of Temperature:

  • Solid to Liquid (Melting/Fusion): Increasing temperature increases the kinetic energy of solid particles. At a specific temperature (melting point), particles overcome the forces of attraction and the solid converts into a liquid.
    • Melting Point: The constant temperature at which a solid melts to become a liquid at atmospheric pressure. It indicates the strength of the force of attraction between particles (higher melting point = stronger forces). Melting point of ice is 0°C (273.15 K, often approximated as 273 K).
    • Latent Heat of Fusion: The amount of heat energy required to change 1 kg of a solid into liquid at its melting point at atmospheric pressure. It's 'latent' (hidden) because the temperature doesn't rise during melting. Particles absorb this energy to overcome inter-particle forces. Water particles at 0°C have more energy than ice particles at 0°C.
  • Liquid to Gas (Boiling/Vaporization): Further heating increases the kinetic energy of liquid particles. At a specific temperature (boiling point), particles gain enough energy to break free from the forces of attraction and change into gas (vapour). Boiling is a bulk phenomenon (entire liquid boils).
    • Boiling Point: The constant temperature at which a liquid starts boiling at atmospheric pressure. Boiling point of water is 100°C (373.15 K or 373 K).
    • Latent Heat of Vaporization: The amount of heat energy required to change 1 kg of a liquid into gas at its boiling point at atmospheric pressure. Steam (water vapour) particles at 100°C have more energy than water particles at 100°C. This is why steam causes more severe burns than boiling water.
  • Gas to Liquid (Condensation): Decreasing temperature (cooling) reduces the kinetic energy of gas particles, causing them to move slower, come closer, and turn into liquid.
  • Liquid to Solid (Solidification/Freezing): Further cooling reduces kinetic energy more, causing particles to lock into fixed positions, forming a solid. Freezing point is generally the same as the melting point.

• (b) Effect of Change of Pressure:

  • Increasing pressure brings gas particles closer. If temperature is also lowered, the gas can liquefy. (Example: LPG cylinders).
  • Sublimation: The change of state directly from solid to gas without passing through the liquid state, and vice-versa (gas to solid is called deposition).
    • Examples: Camphor, ammonium chloride (NH₄Cl), naphthalene balls, iodine, dry ice (solid CO₂).
    • Solid CO₂ (dry ice) turns directly into gaseous CO₂ when pressure is decreased to 1 atmosphere, without becoming liquid. It's used as a cooling agent.

7. Evaporation:

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

8. Units:

• Temperature:
  • SI unit: Kelvin (K)
  • Common unit: Degree Celsius (°C)
  • Conversion: K = °C + 273.15 (often approximated as K = °C + 273)
  • 0°C = 273.15 K
  • 100°C = 373.15 K
  • Note: Temperature in Kelvin is always positive.
• Pressure:
  • SI unit: Pascal (Pa)
  • Common unit: Atmosphere (atm)
  • 1 atmosphere (atm) = 1.01 × 10⁵ Pa
  • Atmospheric pressure is the pressure exerted by the air in the atmosphere. At sea level, it is 1 atm.
• Mass: SI unit: kilogram (kg)
• Volume: SI unit: cubic metre (m³). Common unit: litre (L). 1 L = 1 dm³, 1 L = 1000 mL, 1 mL = 1 cm³. 1 m³ = 1000 L.
• Density: Mass per unit volume (kg/m³ or g/cm³).

Multiple Choice Questions (MCQs)

1. Which of the following phenomena increases on increasing the temperature?
   (a) Diffusion, evaporation, compression of gases
   (b) Evaporation, compression of gases, solubility
   (c) Evaporation, diffusion, expansion of gases
   (d) Evaporation, solubility, diffusion, compression of gases

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. A few substances are arranged in the increasing order of ‘forces of attraction’ between their particles. Which one of the following represents a correct arrangement?
   (a) Water, air, wind
   (b) Air, sugar, oil
   (c) Oxygen, water, sugar
   (d) Salt, juice, air

6. On converting 308 K, 329 K and 391 K to Celsius scale, the correct sequence of temperatures will be:
   (a) 35°C, 56°C, 118°C
   (b) 35°C, 56°C, 119°C
   (c) 56°C, 118°C, 35°C
   (d) 118°C, 56°C, 35°C

7. 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

8. Which of the following substances undergoes sublimation?
   (a) Ice
   (b) Naphthalene
   (c) Common Salt
   (d) Wax

9. Particles of matter possess kinetic energy. With an increase in temperature, the kinetic energy of particles:
   (a) Decreases
   (b) Increases
   (c) Remains unchanged
   (d) First increases then decreases

10. Which of the following has the highest compressibility?
    (a) Solid Carbon Dioxide (Dry Ice)
    (b) Water
    (c) Air
    (d) Iron block

Answers to MCQs:

1. (c) [Temperature increases kinetic energy, thus increasing diffusion, evaporation, and expansion of gases. Compression is easier at low temperatures.]
2. (c) [Gases liquefy under low temperature and high pressure.]
3. (c) [Fluids are substances that can flow. Both gases and liquids exhibit fluidity.]
4. (d) [Earthen pots have pores through which water seeps out and evaporates, causing cooling.]
5. (c) [Forces of attraction: Gas (Oxygen) < Liquid (Water) < Solid (Sugar)]
6. (a) [°C = K - 273. 308-273=35°C; 329-273=56°C; 391-273=118°C]
7. (a) [Higher temperature increases the kinetic energy of surface particles, leading to faster evaporation.]
8. (b) [Naphthalene sublimes directly from solid to gas.]
9. (b) [Temperature is a measure of the average kinetic energy of particles.]
10. (c) [Gases (like air) have large inter-particle spaces and are highly compressible compared to liquids and solids.]

Make sure you revise these concepts thoroughly. Understand the 'why' behind each property and phenomenon, especially latent heat and factors affecting evaporation, as these are frequently tested areas. Good luck with your preparation!