Question 1

Question 1Discuss the three states of matter: solid, liquid and gas on the basis of molecular model.

Accepted Answer

Molecular Model of SolidsThe molecular model of solids is shown in the figure below:Each solid is made up of very tiny particles called molecules that are in a rigid arrangement.The inter-molecular space is very small incase of solids.The molecules in a solid can only vibrate to and fro about their mean positions. They do not leave their positions.The molecules in a solid are closely packed due to strong inter-molecular force of attraction between them.Solids have definite shape and volume.Molecular Model of LiquidsThe molecular model of liquids is shown in the figure below:Each liquid is made up of very tiny particles called molecules that are not in a rigid arrangement.The inter-molecular spaces in liquids are more than that in solids.The molecules in a liquid are less closely packed and their positions are not fixed as they are free to move within the boundary of the vessel in which the liquid is kept.Although the inter-molecular force of attraction is weak as compared to solids but it is sufficient to keep them within the boundary of the vessel.Liquids have definite volume but no definite shape.Molecular Model of GasesThe molecular model of gases is shown in the figure below:Gases are made up of very tiny particles called molecules that are not in a rigid arrangement.In gases the inter-molecular space is maximum and the force of attraction is least as compared to solids and liquids.The position of these molecules are not fixed. The molecules can move randomly anywhere due to weak inter-molecular forces.Gases have neither definite shape nor definite volume.

Question 2

Question 2What do you mean by 'the change of state'? Write the flowchart showing the complete cycle of change of state.

Accepted Answer

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.Flowchart showing the complete cycle of change of state is shown below:

Question 3

Question 3Differentiate between melting point and boiling point, giving atleast one example of each.

Accepted Answer

Sl.No.Melting pointBoiling point1.The temperature at which a solid changes into liquid without further increase in temperature is called the melting point of solid.The temperature at which a liquid changes into vapour without further increase in temperature is called the boiling point of the liquid.2.Ice (solid) changes into water (liquid) at 0°C by absorbing heat.Water (liquid) changes into steam (gas) at 100°C by absorbing heat.

Question 4

Question 4Describe the process of condensation and sublimation with examples.

Accepted Answer

The change from vapour state to liquid state at a constant temperature on releasing heat (or on cooling) is called condensation.Example — Steam (gas) at 100°C condenses to water (liquid) at 100°C on cooling (i.e. by rejecting heat).Sublimation is the process by which a solid when heated directly changes into its vapour (gaseous state) without first changing into liquid.Example — When camphor (solid) is heated it directly changes into its vapours (gaseous state).

Question 5

Question 6Describe an experiment to demonstrate that a substance absorbs heat during melting without change in its temperature.

Accepted Answer

The following experiment demonstrates that a substance absorbs heat during melting without change in its temperature —Take a test tube with some wax in it.Clamp the test tube in a vertical stand and place the test tube in a beaker of water.Place the beaker on a wire gauze which is kept on 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 the figure above.Heat the beaker over the flame of a burner.Record the temperature of the wax from the thermometer after every minute.Observations:Time(in minute)Temperatureof wax (in °C)025130235340445550655755855955106011651270Conclusion: From the above observations, we can conclude that wax melts at 55°C during which heat is supplied but the temperature does not rise. Hence, wax absorbs heat during melting without change in its temperature.

Question 6

Question 7Explain the terms vaporization and boiling point.

Accepted Answer

The change from liquid state to gaseous state on heating at a constant temperature by absorption of heat is called vaporization.The temperature at which a liquid changes into vapour without further increase in temperature is called the boiling point of the liquid.Example — Water (liquid) at 100°C changes into steam (gas) at 100°C by absorbing heat.

Question 7

Question 8Describe an experiment to demonstrate that water absorbs heat during boiling at a constant temperature.

Accepted Answer

The following experiment demonstrates that water absorbs heat during boiling at a constant temperature —Take a beaker and pour some water in it.Place the beaker on a wire gauze placed over a tripod stand.Clamp a thermometer in a vertical stand and insert it in the beaker.Heat the beaker over the flame of a burner.Record the temperature of water after every minute.Observation — The temperature of water gradually rises and when it reaches 100°C, water starts boiling. Once the water starts boiling, its temperature does not rise any further, although heat is still being supplied.Conclusion — From the above experiment we can conclude that, at 100°C water begins to boil and changes into steam by absorbing the heat being supplied to it without further rise in temperature.

Question 8

Question 10Explain with an example that when a liquid evaporates, it takes heat from its surroundings.

Accepted Answer

If some alcohol (or spirit) is poured on some cotton (or wool) wrapped around the bulb of a thermometer, the reading of the thermometer falls. The reason for this observation is that, to evaporate, alcohol requires heat which it absorbs from the cotton wrapped around the thermometer (it's surroundings) producing a cooling effect that is recorded by the thermometer as a fall in temperature.

Question 9

Question 12Describe an experiment to demonstrate the process of sublimation.

Accepted Answer

The process of sublimation is demonstrated by the following experiment —Take some ammonium chloride and powder it.Keep the powder in a china dish.Cover the china dish with an inverted funnel as shown in the figure.Close the end of the funnel with a piece of cotton.Place the china dish on a wire mesh kept on a tripod stand and heat it by a burner.Observations — We will observe that vapours of ammonium chloride are formed in the inverted funnel above the dish. These vapours upon rising, get cooled and change to solid ammonium chloride which gets deposited on the inner walls of the inverted funnel.Conclusion — Ammonium chloride on heating changes directly into gaseous state and when these vapours are cooled they get converted back into solid state. This demonstrates the process of sublimation.

Question 10

Question 1(i)Identify the correct statement.(1) The molecules of water move faster than ice.(2) The molecules are more closely packed in ice than water.(3) The molecules of water vibrate to and fro only but those of ice are free to move within the boundary of the vessel in which it is kept.(4) The molecules have more intermolecular space in ice than in water.(1), (2) and (3)(2), (3) and (4)(1) and (2)all are correct

Accepted Answer

(1) and (2)Reason —(1) Correct because water is in liquid state, so its molecules have more kinetic energy and move faster than those in solid ice.(2) Correct as ice is in solid state where intermolecular spaces between the particles are very less than those of water which is in liquid state.(3) Incorrect since in ice (solid), particles vibrate in fixed positions (to and fro) but in water (liquid), molecules are free to move within the vessel.(4) Incorrect because water has more intermolecular space than ice.

Question 11

Question 5Which 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.

Accepted Answer

The correct options are(a) Solids have definite shape and definite volume.Reason — In solids the inter-molecular space is the least and the molecules remain in their fixed positions due to strong inter-molecular force of attraction so solids have definite shape and definite volume.(b) Liquids have definite volume but no definite shape.Reason — The molecules in liquid are less closely packed, their positions are not fixed and they move freely. Although the inter-molecular force of attraction is weak as compared to solids but it is sufficient to keep them within the boundary of the vessel. So liquids have definite volume but no definite shape.

Question 12

Question 11Why is cooling produced on evaporation of a liquid?

Accepted Answer

During evaporation process a liquid changes into gas by absorbing heat from the surroundings. This results in fall of temperature of the surroundings. So cooling is produced on evaporation of a liquid.

Question 13

Question 13What do you mean by sublimation? Explain with an example.

Accepted Answer

Sublimation is the process by which a solid when heated, directly changes into vapour without first changing into liquid.For example, when ammonium chloride is heated it directly changes into vapour without changing into liquid.

Question 14

Question 14Why does the size of naphthalene balls decrease when left open?

Accepted Answer

Naphthalene balls when left open, directly change into vapour without heating due to sublimation. Hence, with time they become small in size.

Matter

Exercise 1 Long Answer Type Questions

Exercise 1 Objective Type Questions

Exercise 1 Short Answer Type Questions