Bhaskar tiwari ch -1

QUESTION : Why do we observe that the level of water does not change even after dissolving the                            salt in it?
ANSWER:  We observe this because the particles of water have space between them,so when we                            dissolve the salt in it the particles of salt get into the space of water particles.

DATE 05.04.16

                                                         PROPERTIES OF PARTICLES
                        

                      

                    1)    Particles of matter are very small.
                    2 )   The particles of matter are continuously moving,means they have kinetic energy.
                    3 )  The particles of matter have space between them.

DATE 06.04.16

QUESTION :Why solids have fixed shapes?

ANSWER: Solid has a fixed shape and a definite volume. The molecules in a solid are in fixed positions and are close together. Although the molecules can still vibrate, they cannot move from one part of the solid to another part. the force of attraction is very high in solid that is why it maintains its shape.

DATE 07.04.16

QUESTION : Give Reasons
a)Table is hard
    Ans >Table is hard because the force of attraction in its molecules are very high and which results in the close packing of molecules and it is very dense.

b)Diver is able to cut through water.
    Ans> Diver is able to cut water because the water is less denser and force of attraction is also less which results in the distance of molecules. The molecules are loosely packed.

c) Why the smell of hot sizzling food reaches our nose?

Ans> Smell of hot sizzling food reaches our nose because the in hot temperature the molecules move faster which results in reaching the smell of food to our nose very quickly. 

DATE 18.04.16

EXERCISE

Ans 1-

 (a) 298 K

  (b) 646 K

Ans 2- 

 (a) 20*c

 (b) 197*c

Ans 3- 

(a) Naphthalene balls disappear with time as the temperature rises, it gets sublimated in gas without leaving any solid.

  (b) The molecules of perfume gets mixed with air molecules which is the least densest matter , that is why we gets smell of perfume sitting several meters away.

Ans 4-

 Oxygen -------> Water -------> Sugar 

Ans 5-

 (a) Liquid State

  (b) Solid State

    

 (c) Gaseous State

Ans 6-

 (a) (i) At room temperature the force of attraction between the molecules of water is medium that is why it is in liquid form.

                

 (ii) The room temperature (25*c) is higher than freezing point (0*c) which will make it solid and it is less than boiling point (100*c) which will make it gas.

            

(b) (i) At room temperature , the inter molecular force of solid is so high that its molecules gets packed together tightly.

                 

(ii) It has fixed shape and fixed volume.

Ans 7-

 At 273 K or 0*c the ice will give more cooling than water because it can absorb more heat than water due to its latent heat of fusion.

Ans 8-

 Steam will cause more serve burns.

DATE 08.04.16

Latent heat of fusion

The heat required to change 1 kg of solid into liquid completely is known as latent heat of fusion. It is absorbed by a body during a constant temperature process that is specified in some way.

Latent heat of vaporization

 The heat required to change 1 kg of liquid into vaporous at atmospheric pressure is known as the latent heat of vaporization.

Evaporation

 The process of conversion of liquid into vapors is known as evaporation.

DATE 18.04.16

Factors affecting the rate of evaporation

1. Temperature- The rate of evaporation is directly proportional to the rise in temperature . more the temperature more will be the evaporation.

2. Humidity- The rate of evaporation is inversely proportional to the humidity. It means that the more the humidity is the less is the rate of evaporation.

3. Wind speed- The rate of evaporation is directly proportional to the wind speed. It means that more is the wind speed more will be the rate of evaporation.

4. Surface area- The rate of evaporation increases when the surface area increases as when the surface area will be increase the evaporation will also be increased.