TOPICS DISCUSSED IN THE CHAPTER

• Introduction
• Physical Nature of Matter
• Diffusion
• Characteristics of Particles of Matter
• States of Matter
• Change of State of Matter
• Effect of Temperature
  • Latent heat
  • Latent heat of fusion
  • Latent heat of vaporisation
• Effect of change of pressure
•  Evaporation
  • Factors affecting the rate of evaporation
  • Evaporation causes cooling
• Plasma
• Bose-Einstein Condensate

INTRODUCTION

• Anything which occupies space and has mass is called matter. Air and water, sugar and sand, hydrogen and oxygen etc.
• Ancient Indian philosophers said that all the matter, living or non-living was made up of five basic elements (panch tatva): air, earth, fire, sky and water.
• Modern day scientists classify matter in two ways: on the basis of its physical properties and on the basis of its chemical properties.
• On the basis of physical properties, matter is classified as solids, liquids and gases.
• On the basis of chemical properties, matter is classified as elements, compounds and mixtures.

Physical nature of matter

• Matter is made up of particles.
• Everything around us is made up of tiny pieces or particles. The particles of matter are constantly moving (they are in motion).
• The particles which make up matter are atoms and molecules.

Evidence of particles in matter:

• The evidence for the existence of particles in matter and their motion comes from the experiments on diffusion and Brownian motion.

Dissolving a solid in a liquid:

• When a crystal of potassium permanganate is placed in a beaker of water, the water slowly turns purple on its own, even without stirring.
• Both potassium permanganate crystal and water are made up of tiny particles.
• When the potassium permanganate crystal is put in water, its particles separate from one another.
• These purpled coloured particles of potassium permanganate spread throughout water making the whole water look purple.
• Actually, on dissolving, the particles of potassium permanganate get into the spaces between the particles of water.
• So it is concluded that the particles are moving or they are in motion.

Mixing of two gases:

• Air is a colourless gas. Bromine vapour is red-brown in colour, and it is heavier than air.
• A gas jar containing air is placed upside down on a gas jar of bromine vapour.
• We will see that the red brown vapours of bromine from the lower gas jar spread up into air in the upper gas jar. And after some time, the gas jar containing air also becomes completely red-brown in colour.
• Both air and bromine vapours are made of tiny moving particles. The moving particles of bromine collide with each other and bounce about in all directions, due to which they get mixed uniformly. This is another example of diffusion.

The process if diffusion gives us two conclusions about the nature of matter.

1. The matter is made up of tiny particles.
2. The particles of matter are constantly moving.

Characteristics of particles of Matter:

The important characteristics of particles of matter are the following

1. The particles of matter are very small.
2. The particles of matter have space between them.
3. The particles of matter are constantly moving.
4. The particles of matter attract each other.

The particles of matter are very small

The very, very small size of particles of matter can be shown by performing the following experiment by using potassium permanganate and water.

• Take 2-3 crystals of potassium permanganate and dissolve them in 100 ml of water in a beaker. We will get a deep purple coloured solution of potassium permanganate in water.
• Take out approximately 10 ml of this solution and put it into 90 ml of clear water in second beaker. Due to this dilution, the colour of potassium permanganate solution in the second beaker becomes a bit lighter.
• Take out 10 ml of this solution and put it into another 90 ml of clear water in third beaker. The colour of solution will become still lighter.
• Keep diluting the solution like this 5 to 8 times.
• In this way, we get a very dilute solution of potassium permanganate in water but the water is still coloured.
• This experiment shows that just a few crystals of potassium permanganate can colour a large volume of water.
• So we conclude that there must be millions of tiny particles in just one crystal of potassium permanganate, which keep on dividing themselves into smaller and smaller particles.

The particles of matter have space between them:

The spaces between the particles of matter can be shown by performing the following experiment by using water and sugar.

• Take a 100 ml beaker.
• Fill half the beaker with water and mark the level of water.
• Dissolve some sugar (50gm) with the help of a glass rod.
• We will find that the level of sugar solution in the beaker is at the same mark where water level was initially in the beaker.
• When sugar is dissolved in water, its crystals separate into very fine particles. These particles of sugar go into the spaces between the various particles of water due to which there is no change in the volume of water on dissolving sugar in it.
• The fact that there is no change in volume on dissolving sugar in water tells us that there are spaces between the particles of water. 

The particles of matter are constantly moving:

• The best evidence that particles of matter are constantly moving comes from the experiments on diffusion and Brownian motion.
• The particles of matter are constantly moving can be shown by performing the following experiment by using potassium permanganate and water.
• As in above.
• If we carry out this experiment by using hot water in the beaker (or gas jar), we will find that the water turns purple at a faster rate. This is because, on heating, the particles of water and that off potassium permanganate gain kinetic energy and move faster. And due to faster movements, they mix into each other more quickly.

The particles of matter attract each other:

• There are some forces of attraction between the particles of matter which bind them together.
• The force of attraction between the particles of the same substance is known as cohesion.
• If we take a piece of chalk, a cube of ice and an iron nail, and beat them with a hammer, we will find that it is very easy to break the piece of chalk into smaller particles, it requires more force to break a cube of ice, whereas the iron nail does not break at all even with a large force.
• This shows that the force of attraction between the particles of chalk is quite weak; the force of attraction between the particles of ice is a bit stronger whereas the force of attraction between the particles of iron nail is very, very strong.

Note:  In general, the force of attraction is maximum in the particles of solids matter and minimum in the particles of a gaseous matter.
Note: rigid means ‘unbending’ or ‘inflexible’. A stone is rigid because it is unbending or inflexible.
Fluid means a material which can flow easily and requires a vessel to keep it. 

States of Matter

On the basis of physical state, all the matter can be classified into three groups: Solids, Liquids and Gases.

Properties of Solids, Liquids and Gases:

Why Solids, Liquids and Gases have different properties:

• According to the kinetic theory of matter, the particles of matter are in continuous motion and possess kinetic energy.
• Some forces of attraction also exist between the particles of matter. These are called inter particle forces. The forces of attraction tend to hold the particles together and control their movements.

The following properties of particles decide whether a given substance will exist as a solid, a liquid or a gas:

1. The spaces between the particles: the spaces between the particles are the minimum in solids, a little more in liquids, and the maximum in gases.
2. The force of attraction between particles: the forces of attraction between the particles are the strongest in solids, less strong in liquids and negligible in gases.
3. The amount of movement of particles (or kinetic energy of particles): the movement of particles is the minimum in solids, more in liquids and the maximum in gases.

Diffusion:

• The spreading out and mixing of a substance with another substance due to the motion of its particles is called diffusion.
• The diffusion of one substance into another substance goes on until a uniform mixture is formed. For example: diffusion of bromine vapours in air. 
• Diffusion is the property of matter which is based on the motion of its particles. Diffusion occurs in gases, liquids and solids.
• Diffusion is fastest in gases and slowest in solids.
• The rate of diffusion increases on increasing the temperature of the diffusing substance.

Diffusion in Gases:

• Diffusion in gases is very fast. This is because the particles in gases move very quickly in all directions.
• The rate of diffusion of a gas, however, depends on its density. Light gases diffuse faster than heavy gases.
• Example: When we light an incense stick (agarbatti) in a corner of our room, its fragrance spreads in the whole room very quickly due to the diffusion of its smoke into the air.

 Diffusion in liquids:

• Diffusion in liquids is slower than that in gases. This is because the particles in liquids move slowly as compared to the particles in gases.
• Example: The spreading of purple colour of potassium permanganate into water, on its own, is due to the diffusion of potassium permanganate particles into water.
• Note: The gases like carbon dioxide and oxygen are essential for the survival of aquatic plants and animals. The carbon dioxide and oxygen gas present in air diffuse into water, and dissolve in it. The aquatic plants use the dissolved carbon dioxide for preparing food by photosynthesis and aquatic animals use the dissolved oxygen of water for breathing. This is an example of diffusion of gases into a liquid.

Diffusion in solids:

• Diffusion can also takes place in solids. Diffusion in solids is very, very slow process.
• Example: If we write something on a blackboard and leave it uncleaned for a considerable period of time, we will find that it becomes quite difficult to clean the blackboard afterwards. This is due to the fact that some of the particles of chalk have diffused into the surface of blackboard.

The Common Unit of Temperature and SI Unit of Temperature:

• The common unit of measuring temperatures (like melting points, boiling points etc.) is ‘degrees Celsius’ which is written in short form as °C.
• Laboratory thermometers and clinical thermometer are calibrated on Celsius scale of temperature.
• There is another scale of temperature called Kelvin scale of temperature which is used by the scientists mainly for research work. The SI unit of measuring temperature is Kelvin, which is denoted by the symbol K.
• The relation between Kelvin scale and Celsius scale of temperature can be written as:

                             Temp. on Kelvin scale=Temp. on Celsius scale + 273

1. To convert a temperature on Celsius scale to Kelvin scale, we have to add 273 to the Celsius temperature.
2. And to convert a temperature on Kelvin scale to the Celsius scale, we have to subtract 273 from the Kelvin temperature.

Change of State of Matter

• We can change the physical state of matter in two ways:
  • By changing the temperature (heating or cooling).
  • By changing the pressure (increasing or decreasing the pressure).
• These two factors decide whether a given substance would be in a solid, liquid or gaseous state.

Effect of Change of Temperature:

Solid to Liquid Change: Melting

• The process in which a solid substance changes into a liquid on heating, is called on melting or fusion.
• The temperature at which a solid substance melts and changes into a liquid at atmospheric  pressure, is called melting point of substance. For example, the ice melts at a temperature of 0°C to form liquid water, so the melting point of ice is 0°C (zero degree Celsius). At melting point, ice changes its state from solid to liquid.
• Different solids have different melting points. Higher the melting point of a solid substance, greater will be the force of attraction between its particles.
• The melting point of a solid is an indication of the strength of the force of attraction between its particles.
• When a solid substance is heated, the heat energy makes its particles vibrate more vigorously. At the melting point, the particles of a solid have sufficient kinetic energy to overcome the strong forces of attraction holding them in fixed positions and break to form small groups of particles and the solid melts to form a liquid.

 Liquid to Gas Change: Boiling (or Vaporisation):

• The process in which a liquid substance changes into a gas rapidly on heating, is called boiling.
• The temperature, at which a liquid boils and changes rapidly into a gas at atmospheric pressure, is called boiling point of the liquid.
• For example, when water is heated to a temperature of 100 °C (hundred degree Celsius).
• Different liquids have different boiling points.
• The boiling point of a liquid is a measure of the force of attraction between its particles.
• When a liquid is heated, the heat energy makes its particles move even faster. At the boiling point the particles of liquid have sufficient kinetic energy to overcome the forces of attraction holding them together and separate into individual particles. And the liquid boils to form a gas. 

Gas to Liquid Change: Condensation

• The process of changing a gas (or vapour) to a liquid by cooling is called condensation.
• When steam (or water vapour) changes into water on cooling, it is called condensation of steam.
• When a gas is cooled enough, then its particles lose so much kinetic energy that they slow down, move closer together until they start being attracted to each other, and form a liquid.

Liquid to solid change: Freezing

• The process of changing a liquid into a solid by cooling is called freezing.
• For example, when water is cooled, it gets converted into a solid called ‘ice’. This is called freezing of water. Freezing means solidification.

Latent heat:

• The heat energy which has to be supplied to change the state of a substance is called its latent heat.
• Latent heat does not raise (or increase) the temperature. But latent heat has always to be supplied to change the state of a substance .The word ‘latent’ means ‘hidden’.
• The latent heat which we supply is used up in overcoming the forces of attraction between the particles of substance during the change of state. Latent heat does not increase the kinetic energy of the particles of the substance, so the temperature of a substance does not rise during the change of state.

Latent heat is of two types:

1. Latent heat of fusion
2. Latent heat of vaporization.

Latent Heat of Fusion (solid to liquid change):

• The heat which is going into ice but not increasing its temperature, is the energy required to change the state of ice from solid to liquid (water). This is known as the latent heat of fusion of ice (or latent heat of melting of ice).
• The latent heat  of fusion (or melting) of a solid is the quantity of heat in joules required to convert 1 kilogram of the solid (at its melting point) to liquid, without any change in temperature.
• The latent heat of fusion of ice is 3.34×10⁵ joules per kilogram (or 3.34 ×10⁵ j/kg).

Latent Heat of Vaporization (liquid to gas change):

• The latent heat of vaporisation of a liquid is the quantity of heat in joules required to convert 1 kilogram of the liquid (at its boiling point) to vapour or gas, without any change in temperature.
• The latent heat of vaporization of water is 22.5×10⁵ joules per kilogram (or 22.5×10⁵ j/kg).
• Note: It has been found that the burns caused by steam are much more severe than those caused by boiling water though both of them are at the same temperature of 100 °C. This is due to the fact that steam contains more heat, in the form of latent heat, than boiling water.

Sublimation:

The changing of a solid directly into vapours on heating and of vapours into solid on cooling, is known as sublimation. 
image

1. The changing of a solid directly into vapour (or gas) is called sublimation.

2. The changing of vapour (or gas) directly into solid is called sublimation.

• The common substances which undergo sublimation are: Ammonium chloride, Iodine, Camphor, Naphthalene and Anthracene.

• When these solids are heated, their particles move so quickly that they separate completely to form vapour (or gas). And when these vapour (or gas) is cooled, these particles slow down so quickly that they become fixed and form a solid.

 Effect of Change of Pressure:

The physical state of matter can also be changed by increasing the pressure or decreasing the pressure.

• Gases can be liquefied by applying pressure and lowering temperature
• When a high pressure is applied to a gas, it gets compressed (into a small volume), and when we also lower its temperature, it gets liquefied. So, we can also say that gases can be liquefied (turned into liquids) by compression and cooling.
• Ammonia gas can be liquefied by applying high pressure and lowering the temperature.
• Decreasing the pressure and raising the temperature can change the state of matter.
• Solid carbon dioxide (dry ice) is stored under high pressure. When a slab of solid carbon dioxide is kept exposed to air, then the pressure on it is reduced to normal atmospheric pressure (1 atmosphere), its temperature rises, and its starts changing into carbon dioxide gas.

Evaporation:

The process of a liquid changing into vapour (or gas) even its boiling point is called evaporation.

• The wet clothes dry due to evaporation of water present in them. Common salt is also recovered from sea-water by the process of evaporation.
• The process of evaporation can be explained as follows: Some particles in liquid always have more kinetic energy than the others. So, even when a liquid is well below its boiling point, some of its particles have enough energy to break the forces of attraction between the particles and escape from the surface of the liquid in the form of vapour (or gas). Thus the fast moving particles (or molecules) of a liquid are constantly escaping from the liquid to form vapour (or gas).

Factors affecting Evapouration:

The evapouration of a liquid depends mainly on the following factors:

1. Temperature
2. Surface area
3. Humidity
4. Wind speed

Temperature: The rate of evaporation increases on increasing the temperature of the liquid.

Surface area of the liquid: The rate of evaporation increases on increasing the surface area of the liquid. For e.g. If the same liquid is kept in a test tube and in a china dish, then the liquid kept in the china dish evaporate more rapidly.

Humidity of Air: The amount of water present in air is represented by a term called humidity. When the humidity of air is slow, then the rate of evaporation is high, and water evaporates more readily.

Wind Speed: The rate of evaporation of a liquid increases with increasing wind speed.

Cooling caused by evaporation:

• The cooling caused by evaporation is based on the fact that when a liquid evaporates, it draws or takes the latent heat of vaporization from ‘anything’ which it touches. By losing heat, this ‘anything’ gets cooled.
• During hot summer days, water is usually kept in an earthen pot (called pitcher or matka) to keep it cool. The earthen pot has large number of extremely small pores (or holes) in its walls. Some of the water continuously keeps seeping through these pores to the outside of the pot. This water evaporates (changes into vapour) continuously and takes the latent heat required for vaporization from the earthen pot and the remaining water. In this way, the remaining water loses heat and gets cooled.
• Perspiration (or sweating) is our body’s method of maintaining a constant temperature.
• We should wear cotton clothes in hot summer days to keep cool and comfortable.

To Show the Presence of Water Vapour in Air

• There is always some water vapour in the air around us. Water vapour comes into the air from the evaporation of water present in ponds, lakes, rivers and oceans.
• Water vapour is also given out by plants by the process of transpiration. Animals give out water vapour when they breathe out air. All this water vapour goes into the air around us.
• The presence of water vapour in air can be shown by the following experiment:
• Let us take some ice -cold water in a tumbler. Soon we will see water droplets on the outer surface of tumbler. The water vapour present in air, on coming in contact with the cold glass of water, loses energy and gets converted to liquid state, which we see as water droplets.

Plasma and Bose- Einstein Condensate:

• Plasma and Bose- Einstein Condensate are two more states of mater apart from three other discusse dpreviously.
• Scientists now say that there are actually five states of matter: Solid, Liquid, Gas, Plasma and Bose- Einstein Condensate.

Plasma

• Plasma is a mixture of free electrons and ions. Plasma occurs naturally in the stars (including the sun).
• Inside the stars, the temperature is so high that the atoms break up. Some of the electrons break away from the atoms converting the rest of atoms into electrically charged particles called ions. This mixture of free electrons and ions in a star is called plasma.
• The sun and other stars glow because of the presence of plasma in them.
• Plasma can also be made on the earth by passing electricity through gases at very low pressure taking in a glass tube. The fluorescent tubes and neon sign bulbs form plasma when they are switched on.

Bose- Einstein Condensate

• In 1920 Indian physicist Satyendra Nath Bose had done some calculations for a fifth state of matter. Building on it calculations, Albert Einstein predicted a new state of matter- the Bose Einstein Condensate (BEC).
• The BEC is formed by cooling a gas of extremely low density (about one –hundred- thousandth the density of normal air) to super low temperature.