Matter - Chemistry, Class IX

1. What is a matter?

Ans.: Something that occupies space, possesses mass, and offers resistance to any stress is called a matter.

 

2. What is a substance?

Ans.: A definite variety of matter, all samples of which have the same properties is commonly called a substance. For example, sugar is a substance, because even the smallest particle of sugar is sweet.

 

3. What are the physical natures of matter?

Ans.: The physical natures of matter are:

(i) all matter is made up of very small particles.

(ii) the constituents particles in any matter are constantly in motion. Thus, they possess    

      kinetic energy.

(iii) the particles in any matter attract each other. This force of attraction decreases as the distance        between the particles increases.

 (iv) particles of matter have space between them.

 

4. What is intermolecular force?

Ans.: The force of attraction between the constituent particles in any form of matter is called intermolecular force.

 

5. What is diffusion?

Ans.: The intermixing of the particles of two or more substances on their own is called diffusion.

 

6. Write the name of all states of matter.

Ans.: There are three major states of matter: solid, liquid and gas. There are also two another states of matter are: plasma and Bose-Einstein Condensate.

 

7. What are the properties of solids?

Ans.: The properties of solids are:

(i) solids are rigid and incompressible.

(ii) a solid has a definite shape and volume. (iii) solids in general have higher density.

(iv) in solids, intermolecular forces are strong.

 

8. What are the properties of liquids?

Ans.: The properties of liquids are:

(i) liquids have no fixed shape.

(ii) a liquid has a definite volume.

(iii) liquids flow from higher level to lower level.

(iv) liquids have lower density than solids.

 

9. What are the properties of gases?

Ans.: The properties of gases are:

(i) gases have no definite shape and fixed volume.

(ii) gases are highly compressible.

(iii) gases have very low densities.

(iv) gases exert pressure on the walls of the container.

 

10. How can matter change its state?

Ans.: The physical state of any matter can be changed in the following ways:

(i) by changing temperature.

(ii) by changing pressure.

(iii) by changing pressure and temperature both.

 

11. What is melting point?

Ans.: The temperature at which a solid substance gets converted into a liquid is called the melting point.

 

12. What is solidification?

Ans.: The process in which a liquid substance changes into a solid on cooling is called freezing or solidification. E.g. conversion of water to ice is called freezing or solidification of water.

 

13. What is boiling point?

Ans.: The fixed temperature at which a liquid boils is called its boiling temperature or boiling point. The boiling point of a liquid in 1 atmospheric pressure is called normal boiling point. In 1 atmospheric pressure, water boils at100°C. So, at the normal boiling point of water is 100°C , or 373.15 K.

 

14. What is condensation?

Ans.: The process in which vapour, on cooling, gets converted into a liquid is called liquefaction or condensation. Condensation is the reverse of vaporization. For example, the conversion of water vapour into liquid water is called condensation of water vapour. The boiling point and condensation temperature of a pure substance are equal.

 

15. What is latent heat?

Ans.: The heat supplied during melting and boiling remains hidden from the thermometer and is called latent heat. Latent means lying hidden.

 

16. What is the latent heat of fusion?

Ans.: The latent heat of fusion of a substance is the quantity of heat required to convert one unit mass of the substance from solid state to the liquid state at its melting point without any change of temperature.

 

17. Steam at 100°C is a more effective heating agent than water at the same temperature, why?

Ans.: The energy of 1 kg of steam at 100°C is 22.6 x 105 J more than that of water at the same temperature. This means that when 1 kg of steam at 100°C is condensed to 1kg of water at 100°C , heat energy equal to 22.6 x 10⁵ joules is given out. Hence, steam at 100°C is a more effective heating agent than water at the same temperature.

 

18. What is evaporation?

Ans.: The process in which a liquid changes into its vapour at temperatures below its boiling point is called evaporation. Evaporation is an endothermic process. Thus, during evaporation, the liquid absorbs heat from the surroundings or from any other body in contact with it. For example, during the drying of clothes in the sun, the water in the clothes absorbs heat energy of the sunlight.

 

19. What are the factors affecting the rate of evaporation?

Ans.: The rate of evaporation of a liquid depends upon the following factors:

(i) Temperature: The rate of evaporation of a liquid increases with a rise in temperature.

(ii) Surface area: The rate of evaporation of a liquid increases when it is spread over a large area.

(iii) Humidity of the surroundings: When the surrounding contains very small amounts of water

      vapour, evaporation is faster.

(iv) Nature of the liquid: The rate of evaporation also depends upon the nature of the liquid. Some

     liquids evaporate fast, while others evaporate at a slow rate. For example, petroleum, ether,

     alcohol, chloroform etc., evaporate much faster than water.

(v) Wind speed: With an increase in the speed of wind, the moist air is replaced by dry wind. This

     results in faster evaporation and hence faster drying.

 

20. Why does evaporation cause cooling?

Ans.: When the evaporating liquid takes the required heat from the other parts of the liquid, the rest

      of the liquid cools down. It causes cooling of the surroundings. For example, on a hot day, we

      perspire. When this sweat evaporates, it absorbs the required heat from our body, and we feel   

      cool.

 

21. Why should we wear cotton clothes during summers?

Ans.: During summers, we perspire more due to the body mechanism to keep it cool. Cotton is a

      good absorber of water. It absorbs the sweat and exposes it to the atmosphere. This speeds up

      evaporation of the sweat and makes us comfortable.

 

22. Why does water get cooled in an earthen pot?

Ans.: An earthen pot has small pores in its walls. When water is poured into it, some of it seeps

      through these pores to its outer surface. On reaching there, it evaporates. The heat required for evaporation is taken from the earthen pot and from the water in it. As a result, the eater in an earthen pot gets cooled down.

 

23. What is relative humidity?

Ans.: The percentage of the amount of water vapour actually present in a certain volume of the air to

      the amount of water vapour needed to saturate it is called its relative humidity. Relative humidity

      has no unit.

 

24. What is absolute humidity?

Ans.: The maximum limit of the water vapour which could be present in one cubic metre of air at any

       temperature is called the absolute humidity or saturated value.

 

25. What is sublimation?

Ans.: A change of state directly from solid to gas without changing into liquid state is called

      sublimation.

 

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

Ans.: Acetone or petrol or perfume is called volatile liquid and evaporates fast and gain energy from

      our palm or surroundings and evaporate causing the palm to feel cool.

 

27. Show the interconversion of the three states matter.

Ans.:

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

Ans.: Ice at 273 K is more effective in cooling than water at the same temperature because it can

      draw from any other body, 3.35x105¬¬¬ Jkg-1 heat more than the same weight of water at the

      same temperature.

Note: To convert the temperature to Kelvin scale we have to add 273 and to Celsius scale subtract 273 from the given temperature. E.g. 25°C=25+273=298K and 300K=300-273=27°C