Matter in our surroundings: Give reasons to support your answer:

 

The smell of hot sizzling food reaches you several meters away but to get the smell of cold food you have to go close. why?

The kinetic energy of the particles of matter increases with the increase in temperature.

A diver is able to cut through water in a swimming pool due to which property of the matter?

 Being a liquid it has weak inter molecules force of attraction between the molecules.

A gas fills completely the vessel in which it is kept.

 There is negligible forces of attraction between the particles of gas.

We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.

In air, there is lot of empty space between the molecules and the forces between the particles are almost negligible. Hence, we can move our hand in air. However we cannot move our hand in a solid block because there are strong forces of attractions between particles in a solid and there is no empty space between them.  

Liquids generally have lower density as compared to solids but ice floats on water. why?

A substance with lower density than water can float on water. Therefore, ice floats on water. When Water molecules freeze, The hydrogen bonds strengthen and push the other water molecules farther away. Hence, the space between the water molecules increases as it freezes from water.

For any substance why does the temperature remain constant during the change of state?

The heat energy supplied is used up in changing the state of matter and also this heat is used for breaking of several bonds or attractive forces.

Why does a desert cooler cool better on  hot dry day?

The higher temperature on a hot day increases the rate of evaporation of water and the dryness of air (low humidity of air) also increases the rate of evaporation of water. On absorbing energy from hot and dry day when it changes its state to vapor produce a cooling effect. 

How does the water kept in an earthen pot become cool during summer?

The process by which liquid starts to change into vapor phase at any temperature is known as evaporation. An earthen pot has many small pores. Water seeps out through these pores and evaporates from the surface of the pot. … As a result, water kept in earthen pot becomes cool.

How does our palm feel cold when we put some acetone or petrol or perfume on it?

When we put some acetone or petrol or perfume on our palm, it evaporates. During evaporation, particles of the liquid absorb energy from the surface of the palm to compensate for the loss of energy, making the surroundings cool.

Why is ice at 273 k more effective in cooling than water at the same temperature?

Ice at 273 K will absorb heat energy or latent heat from the medium to overcome the fusion to become water. Solid ice changes its state to liquid which produce a cooling effect whereas there is no change in the state of water hence no cooling effect. 

Why perspiration keeps our body cool?

Due to evaporation because when the Sweat evaporates it gains energy from the surroundings of the environment and in this way the whole body becomes cool.

Why do we see water droplets on the outer surface of a glass containing ice cold water?

The water vapour presents in air, on coming in contact with the cold glass of water, loses energy and gets converted to liquid state, which we see as water droplets.

Which property of gas is used in supplying oxygen cylinders to hospitals?

Compressibilty is higher in gases.

At what temperature does solid ice and liquid water co exist together?

0 degree Celsius or 273 K 

Get the notes of this chapter.

ncert pdf