1. Define the term matter. What is it composed of?
Ans. Matter is something which occupies space, has mass and can be perceived by our senses.
Matter is composed of tiny particles called molecules.
2. State three properties of molecules of matter.
Ans. Following are three properties of molecules of matter:
1. Molecules are very small in size of the order of 10-¹⁰ m.
2. They have space between them called as intermolecular space.
3. Molecules are in constant motion as they possess kinetic energy.
3. What do you mean by intermolecular spaces? How do they vary in different states of matter?
Ans. The space between the molecules of matter is called intermolecular space.
It is less in solids, more in liquids and still more in gases.
4. What is meant by intermolecular forces of attraction? How do they vary in solids, liquids and gases?
Ans. The molecules of matter exert a force of attraction on each other called as intermolecular force.
The force of attraction between the molecules of a solid is very strong, while it is less strong between the molecules of a liquid and negligible between the molecules of a gas.
5. Which of the following are correct?
A) solids have definite shape and definite volume.
B) liquids have definite volume but no definite shape.
C) gases have definite volume but no definite shape.
D) liquids have both definite shape and definite volume.
Ans.A) solids have definite shape and definite volume.
B) liquids have definite volume but no definite shape.
These two statements are correct and rest two options are incorrect.
6. Discuss the three States of matter: solid, liquid and gas on the basis of molecular model.
Ans.Molecular model of solids:
1. Made up of very tiny particles-molecules.
Like tiny rigid balls.
2. Inter molecular spacing is very small.
3. Can only vibrate to and fro about their mean positions. They do not leave their positions.
4. Closely packed due to the strong inter-molecular force between them.
*Molecular model of liquids:
1. made up of very tiny particles -molecules.
2. Intermolecular spacing in liquids are more than solids.
3.can move about freely within the boundary of The vessel in which the liquid is kept.
4. less closely packed because the intermolecular forces in a liquid are weak in comparison to that in solids.
*Molecular model of gases:
1. Made up of very tiny particles-molecules.
Like non-rigid balls.
2. Intermolecular spacing is very large.
3. can move about freely in the space available to them.
4. Are wide apart because the intermolecular forces in them are very weak.
7. What do you mean by the change of state?Write the flow chart showing the complete cycle of change of state.
Ans.Change of state:
-the process of change from one state to another state either by absorption or rejection of heat at a constant temperature is called change of state.
Flow chart of change of state of a substance:
8. Differentiate between melting point and boiling point, giving at least one example of each.
Ans. Melting point-the constant temperature at which solid changes into liquid by absorbing heat energy.eg. ice melts at zero degree celsius.
Boiling/vaporization-the process of change from liquid state to gaseous state by absorption of heat at a constant temperature.eg. water boils at hundred degree Celsius.
9. Describe the process of condensation and sublimation with examples.
Ans.
Condensation-the process of change from gaseous state to liquid state by rejection of heat at a constant temperature. Example water vapour condenses into water at hundred degree Celsius.
Sublimation-the process of change from solid state to gaseous state directly by absorption of heat at a constant temperature .eg. ammonium chloride, iodine, camphor, naphthalene and solid carbon dioxide (dry ice).
10. Explain the terms melting and melting point.
Ans. Melting/fusion-the process of change from solid state to liquid state by absorption of heat at a constant temperature.
Melting point-the constant temperature at which solid changes into liquid by absorbing heat energy.
11.describe an experiment to demonstrate that a substance absorbs heat during melting without change its temperature.
Ans. Explain activity 6 and draw figure 1.8
The wax melts at 55 degree Celsius during which heat is supplied, but temperature does not rise. After The melting of whole wax, the temperature begins to rise.energy used in increasing the potential energy of molecules.
,12. Explain the terms vaporization and boiling point.
Ans.Boiling/vaporization-the process of change from liquid state to gaseous state by absorption of heat at a constant temperature.
Boiling point-the constant temperature at which substance boils by absorbing heat energy is called as boiling point. Boiling point of water is 100 degree Celsius.
13. A liquid can change into vapour state:
A) at a fixed temperature- boiling or vaporization
B) at all temperatures- evaporation.
14.some ise is taken in a beaker and its temperature is recorded after each one minute.
The observations are listed below:
from the above observations what conclusion do you draw about the melting point of ice?
Ans. The melting point of ice is zero degree celsius.
Because we know that at a constant temperature, change of state of a substance takes place by absorbing heat energy. Here the temperature remains constant for 5 minutes although heat is provided. so during that time only change in state it takes place.
15.describe an experiment to demonstrate that water absorbs heat during boiling at a constant temperature.
Ans. Activity 8 and figure 1.9 has to be explained and drawn respectively.
the temperature of water rises continuously until the water starts boiling at hundred degree Celsius. When 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 steam. Thus, the boiling point of water is hundred degree Celsius.
16. State A) the melting point of ice and B) the boiling point of water.
Ans.A) the melting point of ice is zero degree celsius.
B) the boiling point of water is 100 degree Celsius.
17. What is evaporation?
Ans. Evaporation is a process by which a liquid changes into vapour.The change of state from liquid to vapour at all temperatures from the surface of a liquid is called evaporation.
18. State three factors which affect the rate of evaporation of a liquid.
Ans. Following are three factors which affect the rate of evaporation of a liquid:
1. The temperature of liquid-the rate of evaporation is higher if the temperature of liquid is high.
2. The area of the exposed surface-the rate of evaporation increases if the area of surface exposed increases.
3. The nature of liquid-volatile liquid with low boiling point evaporates faster than other liquids .
19. Wet clothes dry more quickly on a war dry day than on a cold humid day. Explain.
Ans.wet dry clothes dry more quickly on a warm dry day than cold humid day because , the rate of evaporation is higher if the temperature of liquid is high.
During drying of wet clothes water present in them needs to be converted from liquid state to gaseous state at room temperature. And we know that this process of changing water into gaseous state at all temperatures is called as evaporation. Evaporation depends on the temperature of a liquid. On hot day temperature is high. Show rate of evaporation is high and so, clothes dries up quickly.
20. Water in a dish evaporates faster than in a bottle. Give reason.
Ans. Water in a dish evaporates faster than in a bottle because rate of evaporation increases if the area of surface exposed increases.
While water in a dish has very less surface area, so rate of evaporation is low. And hence it takes longer time to evaporate completely from that bottle.
21.why are volatile liquids such as alcohol and spirit stored in a tightly closed bottles?
Ans.volatile liquids such as alcohol and spirit are stored in tightly closed bottles because they had very low boiling point and evaporation rate is much faster. So ,to stop them from getting evaporated, they are kept in a tightly closed bottles.
22.a certain quantity of water is heated from 20 degree Celsius 200 degree Celsius. Its temperature is recorded after each 1 minute. The observations are:
what conclusion do you draw from the above table about the boiling point of water? Explain.
Ans. The the boiling point of water is 100 degree Celsius.
The process of change from liquid state to to gaseous state by absorption of heat at a constant temperature is called boiling. The constant temperature at which water boils is called as boiling point of water.
Here in this case temperature remains constant at hundred degree Celsius although heat is supplied to it. So in this case the boiling point is 100 degree Celsius.
23. Why is cooling produced on evaporation of a liquid?
Ans.
Evaporation produces cooling. Because during evaporation process heat is absorbed from the surrounding or from a body and as a result of it, the temperature decreases. we get relieved from hot climate.24. Explain with an example that when a liquid evaporates, it takes heat from its surroundings.
Ans.evaporation of sweat from our body helps to maintain the body temperature at 37 degree Celsius or 98.6 degree fahrenheit. When sweat evaporates, it requires heat which takes away from our body. As a result, temperature falls to keep the body at 37 degrees celsius.
25. Give two applications of evaporation.
Ans. Following are two applications of evaporation:
1. Water gets cooled in an earthen pot. Water ships out on the surface through the pores in the pot and it evaporates. The heat required for evaporation is taken from water inside the pot which therefore gets cooled.
2. Doctor advice to put the strips of wet cloth on the fore head of a patient having high fever. Water of the strips evaporates and water takes heat from the body of the patient and thus the temperature of a body decreases.
26. Explain why in hot summer days water remains cool in earthen pots?
Ans.in hot summer days water remains cool in earthen pots because of evaporation taking place from its outer surface. During this process heat is absorbed from the water inside the pot and hence it gets cooled.
27.a patient suffering from high fever is advised to put wet cloth strips on his forehead. Why?
Ans.a patient suffering from high fever is advised to put wet clothes strips on his forehead. Water of the strips evaporates. During evaporation,water takes heat from the body of the patient and does the temperature of his body decreases.
28. What do you mean by sublimation? Explain with an example.
Ans.the process of change of solid directly into gas at a fixed temperature without changing into liquid is called sublimation. For example, when ammonium chloride, iodine, camphor, naphthalene and solid carbon dioxide are heated, they directly changed into their vapours.
You should explain activity 10 and figure 1.11 of your physics book.
29. Why does the size of naphthalene ball decreases when left open?
Ans. The size of naphthalene ball decreases when left open because of sublimation.
Sometimes sublimation and also takes place without heating.moth balls which are used to protect woolen clothes from insects, directly changes into vapour and with time they become small in size.
30. Describe an experiment to demonstrate the process of sublimation.
Ans. Activity 10 and figure you have to write and draw respectively from a physics book.
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