Solution
Short/Long Answer Questions:
1. Define the term matter. What is it composed?
ANSWER- Anything which occupies space and has mass is called matter. Matter composed of molecules.
2. State three properties of molecules of matter.
ANSWER- Three properties of molecules-
i) They are small
ii) They have space between them.
iii) They attract each other.
3. What do you mean by inter-molecular spaces? How do they vary in different states of matter?
ANSWER- The space between the molecules of matter
is called Intermolecular space.
Solid- least intermolecular space
Liquid- less intermolecular space
Gas- most intermolecular space
4. What is meant by inter-molecular forces attraction? How do they vary in solids, liquids, and gases?
ANSWER- The force of attraction between molecules
is called Intermolecular force of attraction.
Solid- intermolecular force strangest
Liquid- intermolecular force is week
Gas- intermolecular force is weakest
5. Which of the following are correct?
(a) Solids have definite shape and definite volume.
(c) Gases have definite volume but no definite
shape.
(d) Liquids have both definite shape and definite
volume.
Ans: Correct: (a) and (b)
6. Discuss the three states of matter: solid, liquid and gas based on molecular model.
ANSWER-
Solids
1. The molecules in a solid are rigid.
2. The molecules in a solid can only vibrate to and fro about their mean positions.
3. The inter-molecular forces are very strong.
4. The molecules in a solid are closely packed.
7. What do you mean by the change of state? Write the flow chart showing the complete cycle of change of state
Answer- the process of change from one state to
another state at constant temperature is called the change of state
8.Differentiate between melting point and boiling point giving at least one example of each
Answer- The fixed temperature at which the solid changes to liquid by absorbing heat is called melting point. Example-ice melts at 0⁰C and the fixed temperature at which the liquid changes to gas by absorbing heat is called boiling point. Example- water boils at 100⁰C.
9. Describe the process of condensation and sublimation with examples
Answer- Condensation- the change from the vapour
state to the liquid state on cooling at the fixed temperature is called
condensation Water vapour condenses at 0⁰C
Sublimation- the process of change of solid directly to the gas without changing in to the liquid is called sublimation. Example - Camphor
10. Explain the terms melting and melting point.
Answer- The process of change of state from solid to liquid at constant temperature is called melting. The fixed temperature at which change of solid to liquid by absorbing heat is called melting point.
11. Describe an experiment to demonstrate that substance absorbs heat during melting without change in its temperature.
Answer- Take a test tube. Put some wax in the
test tube. Clamp the test tube in a vertical stand and place the test tube in a
beaker of water placed on a wire gauze at a tripod stand. Clamp a thermometer
in the same vertical stand and insert the thermometer in the test tube such
that the bulb of the thermometer is inside the wax as shown in Fig. Heat the
beaker over the flame of a burner and record the temperature of the wax after
every minute. Record every minute.
It is observed that in the beginning temperature increases once reaches to 55⁰C, no further change in the temperature for some time as change of state takes place. Conclusion- wax melts at 55⁹C. When change of state takes place, no rise in temperature.
12. Explain the terms vaporization and boiling point.
Answer- The change from the liquid state to the gaseous state on heating at constant temperature is called vaporization. The temperature at which the liquid changes into the vapour without further increase in temperature is called boiling point of the liquid.
13. A liquid can change into vapour state.
(a) at a fixed temperature, and (b) at all temperatures
Name the processes involved in the two cases
From the above observations what conclusion do you draw about the melting point of ice?
Ans: Melting point of ice = 0°C
15. Describe an experiment to demonstrate that water absorbs heat during boiling at a constant temperature. Answer-Take a beaker. Pour some water in the beaker. Place the beaker on a wire gauze placed over the tripod stand. Clamp a thermometer in a vertical stand and insert it in the beaker as shown in Fig. Heat the beaker over the flame of a burner and record the temperature of water after every minute
It is notice that the temperature of water rises continuously till the water starts boiling at 100°C. Once the water starts boiling, its temperature does not rise any further, although the heat is still being supplied. Now the bubbles formed through the water are seen. At this temperature water begins to boil and changes into the steam. Thus, the boiling point of water is 100°C.
16. A certain quantity of water is heated from 20 degree centigrade 200 degree centigrade its temperature is recorded after each one minute the observations are?
Answer- Water boils at 100⁰C.
17. State (a) the melting point of ice and (b) the boiling point of water
Answer- a) Melting point of ice is - 0⁰C
b) Boiling point of water is 100⁰C
18. What is evaporation?
Answer- the change from the liquid state to the vapour state at all temperature from the surface of a liquid is called its evaporation.
19. State three factors which affect the rate of evaporation of a liquid.
Answer-Three factors which affect the rate of evaporation of a liquid-
1 the temperature of liquid
2. the area of surface exposed
3 the nature of liquid.
20. Wet clothes dry more quickly on a warm dry day than on a cold humid day. Explain.
Answer-Wet clothes dry more quickly on a warm dry day than on a cold humid day as the rate of evaporation is higher if the temperature of liquid is high.
21. Water in a dish evaporates faster than in a bottle. Explain
Answer-Water in a dish evaporates faster than in a bottle as the rate of evaporation is higher if area of surface exposed is large.
22. Volatile liquids such as alcohol and spirit are stored in the tightly closed bottles. Explain the reason.
Answer-Volatile liquids such as alcohol and spirit evaporate faster than water is stored in the tightly closed bottles
23. Why is cooling produced on evaporation of a liquid?
Answer-Cooling is produced on evaporation of a liquid because when a liquid changes into vapour, it requires heat. This heat is supplied by the surroundings of the liquid. These results fall in temperature (or cooling)
24. Explain with an example that when a liquid evaporates, it takes heat from its surroundings.
Answer- If a little alcohol (or sanitizer) is poured on the palm, it gives soothing (cooling) sensation.
25. Give two applications of evaporation.
Answer- Two applications of evaporation
1. In summer, water gets cooled in an earthen pot.
2.We often pour tea in a saucer to cooling faster
26. Explain why in hot summer days water remains cool in earthen pots.
Answer-In hot summer days water remains cool in earthen pots because the water seeps out through the pores in the pot and it evaporates. The latent heat required for evaporation is taken from water inside the pot which therefore gets cooled.
27. A patient suffering from high fever is advised to put wet cloth strips on his forehead. Why?
Answer- A patient suffering from high fever is advised to put wet cloth strips on his forehead. The reason is that water of strips evaporates. During evaporation, water takes latent heat from the body of the patient and thus the temperature of his body decreases.
28. What do you mean by sublimation? Explain with an example.
Answer- The process by which solid directly changes to vapour when heated is called Sublimation. Example- camphor.
29. Why does the size of naphthalene balls decrease when left open?
It is noticed that the fumes (i.e., vapours) of
ammonium chloride are seen in the funnel above the dish. These vapours when
rises, get cooled and change to solid ammonium chloride which gets deposited on
the walls of funnel. Thus, ammonium chloride on heating changes directly from
solid to vapour and these vapours on cooling directly changes to solid.
