Chapter 1: Matter in Our Surroundings Exercise Questions & Answers
1Convert the following temperatures to the Celsius scale. (a) 293 K (b) 470 K
Answer:
Using the formula: °C = K – 273
(a) 293 K = 293 – 273 = 20°C
(b) 470 K = 470 – 273 = 197°C
2Convert the following temperatures to the Kelvin scale. (a) 25°C (b) 373°C
Answer:
Using the formula: K = °C + 273
(a) 25°C = 25 + 273 = 298 K
(b) 373°C = 373 + 273 = 646 K
3Give 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.
Answer:
(a) Naphthalene undergoes sublimation—it changes directly from solid to gas without becoming liquid.
(b) Perfume particles diffuse rapidly through air due to high kinetic energy and large intermolecular spaces in gases.
4Arrange the following substances in increasing order of forces of attraction between the particles: water, sugar, oxygen.
Answer: Oxygen < Water < Sugar
Gases (oxygen) have weakest forces, liquids (water) intermediate, and solids (sugar) strongest.
5What is the physical state of water at: (a) 25°C (b) 0°C (c) 100°C?
Answer:
(a) Liquid — room temperature.
(b) Solid or liquid (equilibrium) — melting point; ice and water coexist.
(c) Liquid or gas (equilibrium) — boiling point; water and steam coexist.
6Give two reasons to justify: (a) Water at room temperature is a liquid. (b) An iron almirah is a solid at room temperature.
Answer:
(a) Water has fixed volume but no fixed shape and flows easily.
(b) Iron almirah has definite shape and fixed volume and is rigid and non-compressible.
7Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer:
Ice absorbs latent heat of fusion from surroundings to melt, providing extra cooling. Water at 273 K does not absorb this additional heat.
8What produces more severe burns, boiling water or steam?
Many of the phase changes discussed here (like evaporation/condensation) are methods used to create
Pure Substances and Separating Mixtures
. Continue your learning with the Q&A for Chapter 2.
Answer: Steam causes more severe burns because it contains extra latent heat of vaporisation, which is released when it condenses on the skin.
9Name A, B, C, D, E and F in the following diagram showing change in its state:
Increase heat and decrease pressure
↗ ↖
A B C
SOLID ————→ LIQUID ————→ GAS
D E F
↖ ↗
Decrease heat and increase pressure