ABHISHEK RAI CH-1

MATTER IN OUR SURROUNDINGS

ACTIVITY- 
 Q. Why do we observe that the level of water does not change even after dissolving salt in it??

ANS-  When we dissolve salt in water , the particles of salt get into spaces between particles of water so this shows that the level of water does not change.

HOMEWORK

PROPERTIES OF PARTICLE

1. The particles of the matter are very small in size.

2. The particles of matter are continuously in motion , means they have kinetic energy.

3. The particles of matter have space between them.

Why solids are hard??

ANS- Solids are usually  hard because they are tightly packed together and solids can maintain their shape own.

GIVE REASONS

Q.1. Why is table hard?

ANS- The table is hard because its rigidity is very high and 

compressibility is not shown.

Q.2. Diver is able to cut water?

Ans- Water is fluid , i.e changes its shape when applied force.The diver is able to cut the water by applying force and changing its shape.

Q.3. The smell of hot sizzling food reaches our nose?

ANS- The smell of hot sizzling food reaches our nose as due to high speed of particles and large space between gases show the property of diffusing very fast into other gases.

Homework

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 vapourisation

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

Evaporation

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

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.

EXERCISE

Q1. Convert the following into celsius scale-

(a) 293 K = 293-273 = 20*C 

(b) 470 K = 470-273 = 197*C

Q2. Convert the following into kelvin-

(a) 25*C = 25 + 273 = 298 K

(b) 373*C = 373+273 = 646 K 

Q3. Give reason for the following-

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

Ans- It happen because naphthalene balls sublime and directly changes into vapour state without leaving any solid.

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

Ans- It happens because perfume contain volatile solvent and 

diffuse faster and can reach people sitting several meters away.

Q4. Arrange the following substances in increasing order of forces of attraction between the particles - water, sugar, oxygen.

Ans- Oxygen-water-sugar

Q5. What is physical state of water at-

(a) 25*C= liquid

(b) 0*C= solid or liquid

(c) 100*C= liquid and gas

Q6. Give reason-

(a) Water at room temperature is a liquid.

Ans- Water at room temperature is a liquid because its freezing point is 0*C and boiling point is 100*C.

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

Ans- It is because the melting point of iron is higher than room temperature.

Q7. Why is ice a 273 K more effective in cooling than water a same temperature?

Ans-Ice at 273 K will absorb heat energy or latent heat from medium to  overcome the fusion to become water. Cooling effect of ice is more than water at same temperature because water does not absorb extra heat from medium.

Q8. What produces more severe burns , boiling water or steam?

Ans- Steam at 100*C will produce more severe burns as extra heat is hidden in it called latent heat whereas the boiling water does not have this hidden heat.