Chapter 1 Matter in Our Surroundings
Question 1. Convert the following
temperatures to the Celsius scale.
(a) 293 K (b) 470 K.
Answer: (a) 293 K into °C
293 – 273 = 20°C
(b) 470 K into °C 470 – 273 = 197°C
Question 2. Convert the following
temperatures to the Kelvin scale.
(a) 25°C (b) 373°C.
Answer: (a) 25°C into K
25 + 273 = 298 K
(b) 373°C into K 4 373 + 273 = 646 K
Question 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.
Answer: (a) Naphthalene balls disappear with time without leaving
any solid, because naphthalene balls sublime and directly changes into vapour
state without leaving any solid.
(b) We can get the smell of perfume sitting several metres away because perfume
contain volatile solvent and diffuse faster and can reach people sitting
several metres away.
Question 4. Arrange the following
substances in increasing order of forces of attraction between the particles—water,
sugar, oxygen.
Answer: Oxygen —> water —> sugar.
Question 5. What is the physical
state of water at—
(a) 25°C (bj 0°C (cj 100°C
Answer: (a) 25°C is liquid (b) 0°C is solid or liquid
(c) 100°C is liquid and gas
Question 6. Give 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 at room temperature is a liquid because its
freezing point is 0°C and boiling point is 100°C.
(b) An iron almirah is a solid at room temperature because melting point of
iron is higher than room temperature.
Question 7. Why is ice at 273 K more
effective in cooling than water at the same temperature?
Answer: Ice at 273 K will absorb heat energy or latent heat from
the medium to overcome the fusion to become water. Hence the cooling effect of
ice is more than the water at same temperature because water does not absorb
this extra heat from the medium.
Question 8. What produces more
severe bums, boiling water or steam?
Answer: Steam at 100°C will produce more severe bums as extra heat
is hidden in it called latent heat whereas the boiling water does not have this
hidden heat.
Question 9. Name A, B, C, D, E and F
in the following diagram showing change in its state
Answer: A —> Liquefication/melting/fusion B —>
Vapourisation/evaporation C—>Condensation D—> Solidification E —>
Sublimation F —> Sublimation
