LONG ANSWER QUESTIONS
Q1. Define matter. Give the main characteristics of the different states of matter.
Ans. Matter is anything that occupies volume and has mass. The different states of matter are solids, liquids and gases. Their main characteristics are as given ahead :
(a) Characteristics of solids :
(1) Solids have definite mass, volume and shape.
(2) The particles in a solid state held very closely by strong attractive forces and the empty spaces in them are negligible.
(3) Because of its being rigid, a solid always tends to resist any change in its structure.
(4) The solids are rigid and do not undergo a change in shape easily.
(5) They possess high densities.
(6) They don't show the property of diffusion.
(7) Solids can have any number of free surfaces.
(b) Characteristics of liquids :
(1) Liquids have definite mass and volume but no definite shape.
(2) The molecules of liquid have more vacant spaces as compared to solids.
(3) The attractive forces between the molecules in a liquid state are lesser than those in the solids, they can take the shape of the container in which they are put.
(4) Liquids can expand on heating.
(5) Liquids have lower densities as compared to solids.
(6) Liquids have only one free surface.
(c) Characteristics of gases :
(1) Gases have definite mass but neither definite shape nor definite volume.
(2) There are negligible attractive forces between the molecules of a gas and there are large vacant spaces between the molecules.
(3) They can occupy the whole space available to them.
(4) They show the property of diffusion.
(5) They have very low densities as compared to the solids and liquids.
(6) The molecules in a gas have high kinetic energies and they exert equal pressure in all the directions on the walls of the container.
(7) They are highly compressible.
Q2. What are intermolecular forces ? How are these related to the three states of matter ?
Ans. Intermolecular forces are the forces operating between the particles of a matter.
In solids, the intermolecular forces are large, which keeps the constituent particles quite close to each other. Thus the solids are rigid having high density and incompressible. This also results in highly ordered arrangement of the particles, thus giving a definite or fixed shape to the solids.
In liquids, the intermolecular forces are comparatively weak which are strong enough to keep the liquid in a bulk. But they are not so strong as to give a fixed shape to the liquids. That is why the liquids take the shape of container in which they are put.
In gases, the intermolecular forces are almost negligible. So the constituent particles are free to move in all the direction. That is why gases occupy all the available space.
Q3. Distinguish between solids, liquids and gases.
Ans. Difference between solids, liquids and gases :
They possess definite shape.
They have definite volume.
Solids have very high density.
They are very rigid.
Their particles are most closely packed.
It is very difficult to compress solids.
The attractive forces between their particles is very large.
They show very low thermal expansion.
They can have any number of free surfaces.
Liquids acquire the shape of the container which they occupy.
They have low density.
Their rigidity is low.
Their particles are loosely packed.
The attractive forces between their particles is more than in gases.
Thermal expansion is more than solids.
They have a single free surface.
Gases acquire the shape of container which they occupy.
They are not at all rigid.
There have very loosely packed particles.
They are highly compressible.
Their particles have very high energies.
Gases show high degree of thermal expansion.
They do not possess any free surface.
Q4. What do you mean by interconversion of states of matter ? How is it brought about ?
Ans. The process of change of matter from one state to another is called interconversion of states of matter. This interconversion can be brought about by temperature and pressure.
1. By changing temperature. A solid can be changed into liquid and liquid can be changed into a gas by increasing the temperature. This is because, on increasing the temperature, the kinetic energies of the molecules increase and they are able to move freely. The reverse changes occur on cooling.
For instance, ice changes into water at 0°C and water changes into steam at 100°C.
2. By changing pressure. A liquid starts boiling at a lower temperature and changes into gaseous state, when the pressure is lowered. Similarly by applying high pressure, a gas can be liquified like CO2, which can be liquified at normal temperature by applying a pressure of 70 atmospheres.
Q5. What do you understand by sublimation ? Give an example with an illustration.
Ans. On raising the temperature, i.e. on heating, matter generally changes its state from solid to liquid and from liquid to gas. For example, when we heat ice (solid), it becomes water (liquid). On further heating, the water changes to vapour (gaseous state). But, there are a few substances that change directly from solid state to gaseous state and vice versa, i.e. from gaseous to solid state.
The process of change of state from solid to gas without changing into liquid state or vice versa is called sublimation.
We can illustrate the process in the following manner :
1. Take some ammonium chloride crystals and powder them.
2. Put this powder in a china dish and place it on a stand placed above a burner.
3. Cover the china dish with an inverted funnel and put some cotton plug on the stem of the burner.
4. Heat the china dish.
You will observe that fine ammonium chloride crystals get deposited on the inner walls of the funnel. This clearly means that upon heating, ammonium chloride gets directly converted into vapours which condense on the inner walls of the funnel. Thus, we can successfully illustrated sublimation
Q6. At a given temperature, how are the particles of matter affected with increasing or reducing pressure on the matter ?
Ans. When the pressure is increased, the particles of a matter come closer and if the pressure is reduced, they move apart on. Thus if pressure is increasingly applied on a gas, particles of the gas come closer and closer and finally the gas may change into liquid and then solid form at the same given temperature. The figure given below shows two effect of increasing pressure, i.e. the changing state of matter on applying pressure at a given temperature.
Q7. Describe the factors which affect evaporation.
Ans. Evaporation depends upon the following four factors :
(a) Surface area, (b) Temperature of the system, (c) Wind and (d) Humidity.
(a) Surface area. As evaporation is a surface phenomenon, it depends on the surface area. The escaping of particles from liquid state to vapour state depends on the extent of surface available to them. So, the rate of evaporation increases with surface area and decreases with decrease in surface area, i.e. it is directly proportional to the surface area.
(b) Temperature of the system. As we know, the kinectic energy of the particles depends on the temperature of the system. With increase of surface temperature, the number of particles with larger kinetic energy increases. Thus the chances of escape of particles from liquid to vapour state become greater. Thus, rate of evaporation increases with temperature, i.e. rate of evaporation is directly proportional to temperature.
(c) Humidity. As we know, humidity means the amount of vapour present in the air. At a given temperature, air cannot hold more than a fixed amount of water vapour. So, the rate of evaporation decreases with increase in the humidity of air.
(d) Wind. When speed of the wind increases, more particles of liquid vapour would be carried away from the surface of the liquid. Thus, humidity decreases and as a result, the rate of evaporation increases.
MULTIPLE CHOICE QUESTIONS
Q1. The Panch Tatva do not include
Q2. When we add sugar in water, the sugar particles disappear because
(a) they are invisible
(b) they are extremely small
(c) they get into the spaces between the water particles
(d) Both (b) and (c)
Q3. The intermolecular spaces are maximum in
|(c)gases||(d)Both (b) and (c)|
Q4. Water is ........... at 25°C.
|(c)gas||(d).None of these|
Q5. Which of the following is not a characteristic of liquids ?
|(a).definite shape||(b).definite volume|
Q6. Which of the following can have any number of free surfaces ?
|(c)solid||(d)All of the above|
Q7. The mass per unit volume of a substance is called
|(c).density||(d)None of these|
Q8. The intermixing of particles on their own is called
|(a).free mixing||(b).self mixing|
Q9. 400 K can also be written as
Q10. The freezing point of pure water is
|(c).273 K||(d).0 K|
Q11. Which form of matter is more stable at high temperature ?
|(c).solids||(d)All of the above|
Q12. Which of the following has the lowest density ?
Q13. The rate of diffusion ................. with rise in temperature.
|(c).remains the same||(d).may increase or decrease|
Q14. Which of the following substances is not a solid ?
Q15. Which of the following changes represents sublimation ?
|(a).gas -> liquid||(b).liquid -> gas|
|(c)solid -> liquid||(d).solid->gas|
Q16. Which of the following are fluids ?
|(c)gases||(d).both (b) and (c)|
Q17. Evaporation causes
|(c).no change in temprature||(d).None of these|
Q18. Evaporation of a substance takes place
|(a).above its boiling point||(b).below its boiling point|
|(c).at its boiling point||(d).None of these|
1. (b) 2. (d) 3. (c) 4. (b) 5. (a) 6. (c) 7. (c) 8. (d) 9. (b) 10. (c) 11. (a) 12. (d) 13. (a) 14. (b) 15. (d) 16. (d) 17. (a) 18. (b)