Chem. Ch-1 Matter In Our Surroundings

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           Ch.1 Matter In Our Surroundings


Exercises


Q1. Convert the following temperatures to the celsius scale.
      (a) 293 K              (b) 470 K

A1. (a) *(t)K = (t)°c + 273 
         ⇒  293 = (t)°c +273
         ⇒  (t)°c = 293 - 273
         ⇒  (t)°c = 20°c
       
       (b)  (t)K = (t)°c + 273
          ⇒ 470 = (t)°c + 273
          ⇒ (t)°c = 470 - 273
          ⇒ (t)°c = 197°c
*(t) refers to temperature.

 Q2. Covert the following temperatures to the Kelvin scale.
       (a) 25°c                             (b) 373°c

 A2. (a) (t)K = (t)°c + 273
        ⇒ (t)K = 25 + 273
        ⇒ (t)K = 298 K
        
       (b) (t)K = (t)°c + 273
        ⇒ (t)K = 373 + 273            
        ⇒ (t)K = 646 K

 Q3. 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. 

A3. (a) Naphthalene balls disappear with time without leaving any solid because they  undergo sublimation i.e. they directly convert from solid to gas without converting into liquid state.
       (b) We can get the smell of perfume because of diffusion. Perfume comes out in gaseous state and there is increased diffusion in gases.

Q4. Arrange the following substances in increasing order of forces of attraction between the particles- 

 A4. Oxygen < water < sugar.

 Q5. What is the physical state of water at-
       (a) 25°c                  (b) 0°c                  (c) 100°c

A5. (a) Liquid state.
        (b) Solid state
        (c) Gaseous state

Q6. Give two reasons to justify-
       (a) water at room temperature is liquid.
       (b) an iron almirah is a solid at room temperature.

 A6. (a) Water at room temperature (i.e. around 20°c) is liquid because the boiling point of water is 100°c and its freezing point is 0°c. Thus at any temperature between 0°c - 100°c, water is liquid.                   

 (b)  An iron almirah is solid at room temperature (i.e. around 20°c) because the melting point of iron is 1538°c. Hence at any temperature below 1538°c, iron will be solid.

Q7. Why is ice at 273 K more effective in cooling than water at the same temperature.

A7. Ice at 273 K (0°c) is more effective in cooling because it has latent heat of fusion. The latent heat of fusion of ice is 3.34 × 105 J/kg (Joules/ kilogram). Thus ice will absorb this much heat from its surrounding and hence it cools more effectively than water at the same temperature.

Q8. What produces more severe burns, boiling water or steam?
A8. Steam causes more severe burns than boiling water at 100°c because steam condenses to form water droplets. Water's latent heat of evaporation is 540 kcal/kg. When steam condenses, it releases this extra energy hence causing burns.

 Q9. Name A,B,C,D,E and F in the following diagram showing change in its state.


A9. A- Melting, B- Vapourisation, C- Condensation, D- Solidification (Freezing), E- Sublimation, F-Sublimation
       

Image credit- http://epathshala.nic.in/e-pathshala-4/flipbook/

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