shardendu dwived.roll no.:35

Exercise(matter in our surrounding)

Question1:- Convert the following temperatures to Celsius scale.

      

                       (a) 300 K                                                (b) 573 k

Answer:- Kelvin is SI unit of temperature, where 0°C = 273.16K

                                        (a) 300 K = 300 − 273 Celsius

                                       °C = 27 °C

                                        (b) 573 K = 573 − 273 Celsius

                                      °C = 300 °C

Question2:-  Convert the following temperatures to Kelvin scale.

                                  (a) 25°C                                            (b) 373°C

Answer:- Kelvin is SI unit of temperature, where 0°C = 273.16K

                         (a) 25 °C = 25 + 273 K

                                          = 298 K 

                      (b) 373 °C = 373 + 273 K 

                                            = 646 K

Question3:-Give reason for the following observations. 

                  

(a) Naphthalene balls disappear with time without leaving any solid

Answer:-Naphthalene balls disappear with time because                                  sublimation takes place there and naphthalene balls get                     converted into vapours without coming in its liquid form.

  

(b) We can get the smell of perfume sitting several metres away. 

Answer:- Gaseous particles possess high speed and large spaces between them. Particles of perfume diffuse into these gaseous particles at a very fast rate and reach our nostrils. This enables us to smell the perfume from a distance

Question 4 :-Arrange the following substances in increasing order of forces of attraction between particles−− water, sugar, oxygen.

answer:-                Oxygen < Water < Sugar 
Question 5: What is the physical state of water at - 
(a) 25°C 
(b) 0°C 
(c) 100°C

answer:-  (a) 25°C - Water at 25°C is present in the liquid state.
(b) 0°C - solid or liquid state.
(c) 100°C - vapour or liquid state.

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

answer:-) At room temperature (25 °C), water is a liquid because it has the following characteristic of liquid: 
.
(i) At room temperature, water has no shape but has a fixed volume that is, it occupies the shape of the container in which it is kept.

(ii) At room temperature, water flows

(b) An iron almirah is a solid at room temperature (25 °C) because: (i) it has a definite shape and volume like a solid at room temperature.

 (ii) it is rigid as solid at 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 has less energy than water (although both are at the same temperature). Water possesses the additional latent heat of fusion. Hence, at 273 K, ice is more effective in cooling than water

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

 Answer : Steam has more energy than boiling water. It possesses the additional latent heat of vaporization. Therefore, burns produced by steam are more severe than those produced by boiling water