## शनिवार, 29 जुलाई 2017

### MATTER IN OUR SURROUNDINGS PART-II

(Chapter – end questions)
1. Convert the following temperatures to the celsius scale.

(a) 293 K (b) 470 K.

Ans. a)

b)

2. Convert the following temperatures to the Kelvin scale.

(a)(b).

Ans. a) = 25 + 273 = 298 K

b) = 373 + 273 = 656 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.

Ans. a) Some substances possess the property of sublimation like camphor and naphthalene balls. Such substances directly change from solid to gaseous state without changing into liquid like ice→ water→ water vapour does. Therefore, naphthalene balls disappear with time without leaving any solid.

b) Being a volatile substance (gets evaporated easily) perfumes change from liquid to gaseous state very fast. Those particles mix up with air particles and diffuse to reach our nostrils such that we get the smell of perfume sitting several metres away.

4. Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen.

Ans. Oxygen < water< sugar.

5. What is the physical state of water at—

(a)(b)(c)?

Ans. At water is liquid, at water is solid(ice), at water is gas(water vapour).

6. Give two reasons to justify—

(a) water at room temperature is a liquid.

(b) an iron almirah is a solid at room temperature.

Ans. a) The room temperature is generally always more than and less than and within this range water is a liquid so water at room temperature is a liquid.

b) The melting point of iron is much higher than the room temperature therefore an iron almirah is a solid at room temperature.

7. Why is ice at 273 K more effective in cooling than water at the same temperature?

Ans. While melting ice absorbs latent heat of melting from the surroundings and gets changed into water that makes the cooling effect more intense as compared to water at same temperature.

8. What produces more severe burns, boiling water or steam?

Ans. As compared to boiling water it is observed that steam produces more severe burns since as the steam changes into boiling water it releases heat of condensation which is equivalent to latent heat of water result is more severe burning.

9. Name A, B, C, D, E and F in the following diagram showing change in its state.

states of matter

Ans. A – Fusion (Heating – Melting)

B – Vaporisation

C – Cooling – Condensation (Liquefaction)

D – Cooling – Freezing (Solidification)

E – Sublimation

F – Solidification