Matter in Our Surroundings
NCERT Solutions • Class 9 Science • Chapter 1Chapter Exercises
1. Convert the following temperatures to the celsius scale.
(a) 293 K (b) 470 K
(a) 293 K (b) 470 K
Formula: $T(^\circ C) = T(K) – 273$
(a) $293 \text{ K} = 293 – 273 =$ $20^\circ \text{C}$
(b) $470 \text{ K} = 470 – 273 =$ $197^\circ \text{C}$
(a) $293 \text{ K} = 293 – 273 =$ $20^\circ \text{C}$
(b) $470 \text{ K} = 470 – 273 =$ $197^\circ \text{C}$
2. Convert the following temperatures to the kelvin scale.
(a) $25^\circ \text{C}$ (b) $373^\circ \text{C}$
(a) $25^\circ \text{C}$ (b) $373^\circ \text{C}$
Formula: $T(K) = T(^\circ C) + 273$
(a) $25^\circ \text{C} = 25 + 273 =$ $298 \text{ K}$
(b) $373^\circ \text{C} = 373 + 273 =$ $646 \text{ K}$
(a) $25^\circ \text{C} = 25 + 273 =$ $298 \text{ K}$
(b) $373^\circ \text{C} = 373 + 273 =$ $646 \text{ K}$
3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
(a) Reason: Sublimation
Naphthalene undergoes sublimation, a process where a solid changes directly into gas without passing through the liquid state. Therefore, it disappears over time without leaving any solid residue.
Naphthalene undergoes sublimation, a process where a solid changes directly into gas without passing through the liquid state. Therefore, it disappears over time without leaving any solid residue.
(b) Reason: Diffusion
Perfume particles turn into gas/vapour rapidly. These gas particles move at high speeds and have large spaces between them. They mix with air particles and reach us through the process of diffusion.
Perfume particles turn into gas/vapour rapidly. These gas particles move at high speeds and have large spaces between them. They mix with air particles and reach us through the process of diffusion.
4. Arrange the following substances in increasing order of forces of attraction between the particles — water, sugar, oxygen.
Order: Gas < Liquid < Solid
1. Oxygen (Gas) – Negligible force of attraction.
2. Water (Liquid) – Intermediate force of attraction.
3. Sugar (Solid) – Strongest force of attraction.
Increasing Order: Oxygen < Water < Sugar
1. Oxygen (Gas) – Negligible force of attraction.
2. Water (Liquid) – Intermediate force of attraction.
3. Sugar (Solid) – Strongest force of attraction.
Increasing Order: Oxygen < Water < Sugar
5. What is the physical state of water at — (a) $25^\circ \text{C}$ (b) $0^\circ \text{C}$ (c) $100^\circ \text{C}$?
(a) At $25^\circ \text{C}$: Liquid (Room temperature).
(b) At $0^\circ \text{C}$: Solid (Ice) or Liquid (Water). This is the melting point of ice.
(c) At $100^\circ \text{C}$: Liquid or Gas (Steam). This is the boiling point of water.
(b) At $0^\circ \text{C}$: Solid (Ice) or Liquid (Water). This is the melting point of ice.
(c) At $100^\circ \text{C}$: Liquid or Gas (Steam). This is the boiling point of water.
6. Give two reasons to justify —
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
(a) Water is a liquid because:
1. It has a fixed volume but no fixed shape (takes the shape of the container).
2. It can flow (fluidity).
1. It has a fixed volume but no fixed shape (takes the shape of the container).
2. It can flow (fluidity).
(b) Iron almirah is a solid because:
1. It has a fixed shape and a fixed volume.
2. It is rigid and cannot be compressed.
1. It has a fixed shape and a fixed volume.
2. It is rigid and cannot be compressed.
7. Why is ice at 273 K more effective in cooling than water at the same temperature?
Latent Heat of Fusion
Ice at 273 K ($0^\circ \text{C}$) absorbs extra heat energy from the medium to overcome the forces of attraction between particles and convert into water. This extra heat is called the Latent Heat of Fusion.
Water at 273 K already possesses this heat energy. Therefore, ice absorbs more heat from the surroundings than water at the same temperature, causing more effective cooling.
Ice at 273 K ($0^\circ \text{C}$) absorbs extra heat energy from the medium to overcome the forces of attraction between particles and convert into water. This extra heat is called the Latent Heat of Fusion.
Water at 273 K already possesses this heat energy. Therefore, ice absorbs more heat from the surroundings than water at the same temperature, causing more effective cooling.
8. What produces more severe burns, boiling water or steam?
Latent Heat of Vaporisation
Steam produces more severe burns.
Reason: Steam particles at $373 \text{ K} (100^\circ \text{C})$ have more energy than water particles at the same temperature. This is because steam has absorbed extra energy in the form of Latent Heat of Vaporisation. When steam hits the skin, it releases this massive amount of extra heat energy, causing severe burns.
Steam produces more severe burns.
Reason: Steam particles at $373 \text{ K} (100^\circ \text{C})$ have more energy than water particles at the same temperature. This is because steam has absorbed extra energy in the form of Latent Heat of Vaporisation. When steam hits the skin, it releases this massive amount of extra heat energy, causing severe burns.
[Image of interconversion of states of matter diagram]
9. Name A, B, C, D, E and F in the following diagram showing change in its state.
- A Solid $\rightarrow$ Liquid: Fusion (or Melting)
- B Liquid $\rightarrow$ Gas: Vaporisation
- C Gas $\rightarrow$ Liquid: Condensation
- D Liquid $\rightarrow$ Solid: Solidification
- E Solid $\rightarrow$ Gas: Sublimation
- F Gas $\rightarrow$ Solid: Sublimation (or Deposition)
Group Activity: Particle Movement Model
Concept Demonstrated: The model demonstrates how particle motion changes with energy.
Observations:
• Tugging Slowly (Solid): Seeds vibrate in fixed positions. Represents solids where particles vibrate but don’t move freely.
• Tugging Moderately (Liquid): Seeds move around each other but stay within the jar’s lower volume. Represents liquids.
• Tugging Rapidly (Gas): Seeds fly apart and hit the walls of the jar. Represents gases where particles move randomly at high speed.
Concept Demonstrated: The model demonstrates how particle motion changes with energy.
Observations:
• Tugging Slowly (Solid): Seeds vibrate in fixed positions. Represents solids where particles vibrate but don’t move freely.
• Tugging Moderately (Liquid): Seeds move around each other but stay within the jar’s lower volume. Represents liquids.
• Tugging Rapidly (Gas): Seeds fly apart and hit the walls of the jar. Represents gases where particles move randomly at high speed.