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Matter

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Published in: Physics
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Physics for Class 8 students of ICSE and CBSE.

Aritra D / Kolkata

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Qualification: M.A (Rabindra Bharati University - [RBU], Kolkata - 2005)

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  1. Chapter 1 Chapter Objectives Matter In this chapter, you will learn about: Particle or Kinetic Theory of Matter States of Matter Energy Content in the Three States of Matter Change of State of matter using the Kinetic Theory Nistha was playing with an ice-cube. In a few minutes, the ice melted into water.. How did that happen? INTRODUCTION Recapitulating, in our previous books we learnt that anything that occupies space and has mass is known as matter. We have also learnt that matter is made up of millions of small particles that are known as molecules, which are held to each other by forces of attraction. In some cases, these forces of attraction are very strong, causing the molecules to be held more closely to each other. This is witnessed in solids. In liquids, the forces of attraction are comparatively less strong and so they are less closely held, allowing liquids to flow easily. The strength of inter-molecular forces of attraction of gases is even less allowing them to be more free-flowing than liquids. Both in liquids and gases (collectively known as fluids because they can flow), the molecules, therefore, move randomly in different directions. solid ordered arrangement, molecules in contact liquid some disorder, molecules in contact gas complete disorder, molecules not in contact . Teaching Tip: The children should be made conceptually clear about what matter is and what its characteristics are. They should also be aware of the smaller particles of matter that include molecules, atoms and sub-atomic particles. PARTICLE OR KINETIC THEORY OF MATTER We must also remember that the movement of molecules is a phenomenon known as Brownian Motion and was first observed by the botanist, Robert Brown. This discovery by Brown led to the validation of the Particle Theory of Matter, also known as the Kinetic Theory of Matter. This Theory states that,
  2. all matter consists of very small particles (these may be molecules, atoms and ions); these particles are always in a constant state of motion; there is space between the particles, allowing for their movement. This space is known as inter- particle (or, molecular) space; the energy in the particles cause their motion and this energy is known as Kinetic Energy; this energy increases with the increase in temperature, causing them to move even more vigorously; the particles also experience inter-particulate forces of attraction (inter-molecular forces of attraction). These forces of attraction are of two types: Force of Cohesion and (ii) Force of Adhesion; the forces of attraction are less when the inter-particle (or, molecular) space is large. F Paper Fiber Ad hesion Cohesion STATES OF MATTER In the earlier classes we have also learnt that matter can neither be created, nor destroyed; it can only be transformed from one state to another. Again, there are three states of matter: solids (very little inter- particle space and so very dense and compact in shape), liquids (inter-particle space larger than that of solids and so less dense and less compact, allowing free flow) and gases (inter-particle space is very large and so this state is the least dense and least compact, allowing even greater freedom of movement than that of liquids). INFO HUB There are two more states of matter that do not exist in natural conditions on earth: the plasma state and the Bose- Einstein Condensate state. The plasma state consists of highly charged particles possessing extremely high kinetic energy. On earth it can be seen in glow-signs and CFLs whereby gases begin to emit light when highly charged particles ionise them. In the universe, this state can be seen in starts which are superheated balls of plasma. The Bose-Einstein Condensate state was first conceived by Satyendra Nath Bose whose theory was recognised by Albert Einstein. According to this theory if any matter is cooled to Absolute Zero then the particles cease to move about as there is no energy left in them any longer. They then form a clump and behave like a single particle. This state was first witnessed in the laboratory in the 1995 by cooling particles (atoms) of rubidium. As the inter-particle space in solids is very less, the particles tend to collide with each other regularly, without at all deviating from their mean positions. The collision of particles helps in the faster transmission of sound (a form of kinetic energy) in comparison to fluids. Even heat is transmitted in solids with the help of the collision of particles (known as conduction). On a larger scale, these collisions of particles in solids can be felt in the form of vibrations. In case of liquids, the particles collide with each other with lesser vigorous because of more inter- particle space. Consequently, sound travels slower in liquids when compared to solids but more in comparison to gases. In liquids, the particles absorb heat and become lighter, causing them to rise
  3. upwards and allowing the cooler and heavier particles to move downwards (known as convection). The particles become lighter because their mass remains the same but their volumes increase and the densities decrease. Since gases have the largest inter-particle space, the movement of their particles is less vigorous and so, sound travels the slowest in gases. The gas particles play a similar role to that of liquid particles in the transfer of heat. ENERGY CONTENT IN THE THREE STATES OF MATTER In the beginning of this chapter, we learnt that solids are denser than liquids and gases. We also learnt that the more energy is absorbed by particles, the more vigorously do they move. So the density of solids requires greater amounts of energy from outside to make the particles move than it is required for liquids or gases because the energy present in the particles is not enough. So, the energy content of solids is lesser than both of liquids and of gases, while that of liquids is lesser than that of gases. In the same way, the amount of heat absorbed when a solid is transformed to a liquid is greater than when a liquid is transformed into a gas. Here, an interesting phenomenon needs to be noted. The heat that is present in solid, liquids and gases, is hidden or latent and cannot be measured by a change of temperature. Thus, at the same temperature, a substance can exist as both a solid and a liquid or a liquid and a gas. For example, water at OOC contains more heat in the liquid form than in the solid form. Therefore, ice at OOC produces a greater cooling effect by absorbing more heat than water does at OOC. The 'Latent Heat', as mentioned above, is of two kinds: Latent Heat of Fusion and Latent Heat of Vaporisation. The Latent Heat of Fusion results in the melting of a solid or freezing of a liquid. When a solid melts, it absorbs the latent heat and when a liquid freezes, it releases latent heat. The Latent Heat of Vaporisation results in the vaporisation of a solid (sublimation) or a liquid and condensation of a vapour into liquid or solid (de-sublimation or deposition). Camphor and Iodine are solids that can sublimate. CHANGES OF STATES OF MATTER USING THE KINETIC THEORY Before discussing the changes of states of matter, it is important to recapitulate and understand two things that we learnt in the beginning of this chapter. Firstly, we learnt that there are two kinds of inter-particulate forces of attraction (Forces of Cohesion and Forces of Adhesion); and secondly, that as the energy increases with the increase in temperature, the particles tend to move with greater vigour. Now, what are these Forces of Cohesion and Adhesion? Forces of Cohesion are experienced between particles of the same substance. For example, the forces of attraction experienced between two molecules of iron.
  4. Forces of Adhesion are experienced between molecules of different substances. For example, the forces of attraction that exist between glue and paper, helping them to stick to one another. These forces can be weakened and overcome by the application of heat energy, causing them to move more vigorously and, thus, away from each other. When this happens, the nature of the matter undergoes a change and so solids are transformed to liquids and gases, and liquids are transformed into gases. The reverse phenomenon happens with the release of energy in the form of heat, leading to a drop in temperatures. The drop in temperatures results in gases being transformed to liquids and liquids to solids. It also causes the strengthening of the Forces of Cohesion and Adhesion. Phase Changes Gas Deposition Sublirnatio Liquid Solid fV1elting Vaporisation: Vaporisation is the process of change of state from the liquid to the gaseous. It is of two types — boiling and evaporation. Boiling: The phenomenon of a liquid changing into a gas at a particular temperature, is known as boiling or vaporisation. This happens because, as said earlier, with the increase in temperature of a liquid, the lighter and heated up molecules rise to the upper levels and the heavier cooler molecules sink below. After a point of time, all the molecules are in a condition when they are equally hot and then they begin to escape into the atmosphere by overcoming the forces of attraction (cohesion or adhesion). The temperature at which a liquid changes into a gas is known as the Boiling Point and remains constant but the heat absorption continues in the form of Latent Heat. The Boiling Point of water is 1000C or 2120F. Evaporation: In evaporation, the change of state from liquid to gaseous can happen at any temperature below the boiling point. Evaporation does not depend only upon the change in temperature as it is also assisted by the wind condition above the surface of the liquid. The water of the seas and oceans evaporate throughout the day and is increased in windy conditions. Melting or Fusion: Melting or fusion is the phenomenon whereby, a solid is changed into a liquid at a particular temperature by the absorption of the Latent Heat of Fusion. With the application of heat, the particles of the solid start moving vigorously and more freely. At a particular point, with the temperature remaining constant, heat continues to be absorbed and gradually the solid changes into a liquid. This temperature is known as the Melting Point. For example, the melting point of ice is OOC. Sublimation: There are some substances, which change directly into the gaseous state from the solid state, without undergoing the stage of melting. The process of directly changing from the solid to the gas is known as sublimation. Substances that sublimate easily include naphthalene, camphor, iodine and
  5. dry ice (solid carbon dioxide). This happens because the molecules on the surface of such solids are able to overcome the forces of attraction and therefore escape easily into the atmosphere. Dry Ice subliming Deposition or de-sublimation: This is the reverse of the process of sublimation. Here, a gas solidifies directly without going through the liquid stage when it undergoes a reduction of temperature. The best example of Deposition is the formation of frost, where, in extreme cold conditions, the air solidifies directly in contact with a cold surface. Condensation: Condensation is the process of change of state of a gas to a liquid upon the reduction of temperature. With the decrease in temperature of a gas, the movement of the liquid particles gets reduced and it becomes more rigid. Gradually, with even further cooling, the gas changes into a liquid. The temperature at which a gas changes into a liquid is known as the Condensation Point and is the same as the Boiling Point. Thus, this process is the reverse of the process of boiling. CONDENSATION Solidification or Freezing: This process is the reverse of the process of melting. Here, a liquid undergoes cooling by the loss of heat and ultimately solidifies. As heat is lost, the particles of the liquid move about with decreasing freeness and ultimately reach a point of rigidity where they can move about only to collide with each other. The temperature at which this takes place is known as the Freezing Point and is the same as the Melting Point of the substance. INFO HUB Solids It has a definite shape and a definite volume. The particles in a solid are rigid and closely packed. The particles can only vibrate to and fro from their mean position. The inter-particle forces are very strong. Cannot flow. Liquids It has a definite volume takes the shape of container. The particles in a liquid non-rigid. The particles of a liquid but the are can move within the boundary of the surface of a liquid. The inter-particle forces are weaker than that of solids but stronger than gases. Can flow. Gases Gases have neither definite shapes nor definite volumes. They take the volume and shape of the container. The particles in a gas are non- rigid. The particles of a gas can move freely in space. The inter-particle forces are very weak. Can flow.
  6. KEY TERMS Matter: Anything that has mass and occupies space Particle: Molecule, atom or sub-atomic particle Intermolecular forces of attraction: The force of attraction between the atoms or molecules of matter Kinetic Energy: The energy that causes the motion of the particles Latent Heat: The heat that is hidden in solids, liquids and gases but cannot measured by change of temperature Forces of Cohesion: Forces of attraction experienced between particles of the same substance Forces of Adhesion: Forces of attraction experienced between particles of different substances Vaporisation: The process of change of state of a liquid to a gas Boiling: The phenomenon of a liquid changing into a gas at a particular temperature. Evaporation: The phenomenon of a liquid changing into a gas at any temperature below the boiling point Melting or Fusion: The phenomenon of change of a solid to a liquid at a particular temperature Sublimation: The phenomenon of change of a solid to a gas directly without changing to liquid Deposition or De-sublimation: The reverse of Sublimation, where a gas changes directly to a solid without changing into a liquid Condensation: The phenomenon of the change of state of a gas to a liquid upon the reduction of temperature Solidification or Freezing: The phenomenon where a liquid changes to a solid with reduction of temperature QUICK NOTES The movement of molecules is a phenomenon known as Brownian Motion and was first observed by the botanist, Robert Brown. Particles of matter are always in a constant state of motion. There is space between the particles, allowing for their movement. This space is known as inter-particle (or, molecular) space. The energy in particles cause their motion and this energy is known as Kinetic Energy. If the intermolecular force between the particles is weak, then the space between two adjacent particles will be more. this energy increases with the increase in temperature, causing them to move even more vigorously. The heat that is present in solid, liquids and gases, is hidden or latent and cannot be measured by a change of temperature. **** RUN-THROUGH **** I. Very Short Answer Questions A. Tick the correct answer.
  7. 1. Which of the following are particles of matter? a. Molecules b. Atoms c. Ions 2. Who among the following discovered the Brownian Motion? a. Dan Brown c. Both of them b. Robert Brown 3. Which of the following are transmitted faster by solids? a. Heat b. Light c. Sound 4. Collisions of particles in solids can be felt in the form of a. Vibrations b. Buffering c. Stammering d. All of these d. None of them d. Both (a) and (c) d. All of these 5. When particles rise up by absorbing heat, allowing cooler particles to come down, the process is called a. Radiation b. Conduction c. Convection d. None of these 6. At the same temperature, a substance can exist in both the solid and liquid conditions. a. True b. Partly true c. False d. Not sure 7. Latent Heat of Fusion results in a. Melting of a solid only c. Both (a) and (b) 8. Solids that can sublimate are a. Camphor b. lodene b. Freezing of a liquid only d. None of these c. Neither (a) and (b) d. Both (a) and (b) 9. The Boiling Point of Water is a. loooc 10. Dry Ice is a. Liquid Nitrogen b. 2120F b. Snow c. Both c. Sugar d. Neither d. Solid Carbon Dioxide B. Choose the correct option and fill in the blanks. 1. The change of a liquid to a gas below boiling point is (evaporation/vaporisation). 2. Latent Heat of (Fusion/Vaporisation) is the phenomenon whereby a liquid is converted into gas with temperature remaining constant. 3. The best example of (Deposition/Sublimation) is the formation of frost, where, in extreme cold conditions, the air solidifies directly in contact with a cold surface. 4. Condensation Point is the same as the (Boiling/Melting) Point. (Zoologist/Botanist). 5. Robert Brown was a 6. (Matter/Molecule) from one state to another. can neither be created, nor destroyed; it can only be transformed 7. The inter-molecular forces of attraction are also known as particulate/inter-spatial) forces of attraction. (inter-
  8. 8. In liquids, the particles absorb heat and become lighter, causing them to rise upwards and allowing the cooler and heavier particles to move downwards known as (conduction/convection). C. State True or False. Correct the false statements. 1. Matter can always be destroyed and created. 2. Liquids and gases are called fluids because they can flow. 3. Robert brown was a chemist. 4. All matter consists of molecules, atoms and ions. 5. The space between the particles, allowing their movement, is known as inter-molecular space. 6. The energy that causes the motion of particles is known as Potential Energy. 7. The particles in solids do not collide frequently and always deviate from their mean position. 8. Sound is a form of Potential Energy. D. Sort the following in correct columns. Definite shape and volume, Particles can move within the boundary of the surface, Weakest inter-particle forces, Cannot flow, Particles can only vibrate around their mean positions, Have a definite volume and take the shape of the container, Have no definite shape or volume, Particles can move freely in space, Can flow, The particles are rigid and strongly-packed Solids Liquids Gases E. Give one example of each of the following: 1. Force of Cohesion 2. Force of Adhesion 3. Evaporation 4. Sublimation 5. Deposition or de-sublimation F. Define the following: 1. Force of Cohesion 2. Force of Adhesion
  9. 3. Latent Heat of Fusion 4. Latent Heat of Vaporisation 5. Vaporisation 6. Boiling 7. Evaporation 8. Melting or Fusion 9. Condensation 10. Freezing or solidification G. Complete the concept map. States of Matter Liqquids (bottom right figure) Solids Packing of particles Movement of particles nstead of 'Packin of articles' lease inse top figure) Gases (bottom left figure) articles' lease insert 'inter- er co article s ace' and instead of 'movement o Il. Short Answer Questions A. Give reasons. 1. Water and ice can both exist at OOC. 2. Solids can vibrate. 3. Sound travels faster through solids than through liquids and gases. 4. Heat transfer in liquids is slower than that of liquids. 5. The drop in temperatures results in gases being transformed to liquids and liquids to solids. B. Distinguish between: 1. Forces of Adhesion and Cohesion 2. Vaporisation and Evaporation
  10. 3. Vaporisation and Boiling 4. Condensation and Solidification 5. Condensation and Deposition 6. Melting and Sublimation 7. Sublimation and Vaporisation 8. Melting and Vaporisation C. Answer the following questions. 1. What is the Brownian Motion? 2. Write about the inter-molecular forces of attraction. 3. Why does heat and sound get transferred in solids faster than that in liquids? 4. Why don't gases have a definite shape and volume? 5. Why do solids require more energy compared to liquids and gases for the movement of particles? 6. What is Latent Heat? 7. When does matter actually undergo a change of state? 8. How is frost formed? D. Complete the following sentences. 1. Five states of matter are 2. Liquids take the shape of the container because 3. Convection occurs when 4. Examples of solids that sublimate are 5. Dry Ice is 6. Evaporation does not depend only upon Ill. Long Answer Questions 1. With the help of a diagram, explain the molecular arrangement of the states of matter. 2. What is the Kinetic Theory of Matter? 3. Explain the process of Convection using the Particle Theory of Matter. 4. Explain the process of Conduction using the Kinetic Theory of Matter. 5. How are Forces of Adhesion and Cohesion different from each other? 6. With the help of a diagram, explain the changes of state of matter. 7. Draw a schematic diagram showing the different changes of states of matter. IV. Challenge
  11. 1. Why are the more effective fuels liquid or gaseous in nature? 2. Why are we asked to keep deodorants away from heat sources? VI. Enrichment 1. Library Research Find out about rocket fuels and discuss them in the context of the Kinetic Theory of Matter. 2. Know Your Scientist Satyendra Nath Bose — Physicist Satyendra Nath Bose, born on January 1, 1894, in Calcutta, India, discovered what became known as bosons and went on to work with Albert Einstein to define one of two basic classes of subatomic particles. Much of the credit for discovering the boson, or "God particle," was given to British physicist Peter Higgs, much to the chagrin of the Indian government and people. He wrote a paper in 1924 in which he derived Planck's quantum radiation law without referencing classical physics—which he was able to do by counting states with identical properties. The paper would later prove seminal in creating the field of quantum statistics. Bose sent the paper to Albert Einstein in Germany, and the scientist recognized its importance, translated it into German and submitted it on Bose's behalf to the prestigious scientific journal Zeitschrift für Physik. The publication led to recognition, and Bose was granted a leave of absence to work in Europe for two years at X-ray and crystallography laboratories, where he worked alongside Einstein and Marie Curie, among others.

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