Lakshay Gangwal Roll no. – 804 Class - IX

 As we look at our surroundings, we a large variety of things with different shapes,sizes and textures. Everything in the universe is made up of material which scientists have named “matter”. The air we breath, the food we eat, stones, clouds, stars, plants and animals, even a small drop of water or a particle of sand – everything is matter. Humans have been trying to understand their surroundings.

 Early Indian philosophers classified matter in the form of 5 basic elements-the “panch tatva”- air, earth, fire, sky and water. Modern scientists have evolved two types of classification of matter based on their physical properties and chemical nature.

 Anything which occupies space and has mass is called matter.

 For a long time, two schools of thought prevailed regarding the nature of matter. One school believed matter to be continuous like a block of wood, whereas, the other thought that matter was made up of particles like sand. Let us perform an activity to decide about the nature of matter – is it continuous or particulate ?

 1) The particles of matter are very, 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.

 Activity - 2 :-  Take 2-3 crystal of potassium permanganate and dissolve them in 100 ml of water.  Take out approximately 10 ml of this solution and put it into 90 ml of clear water.  Take out 10 ml of this solution and put it into another 90 ml of clear water.  Keep diluting the solution like this 5 to 8 times.

 This experiment shows that just a few crystals of potassium permanganate can colour a large volume of water (about 1000 l ) so we conclude that there must be millions of tiny particles in just on crystal of potassium permanganate, which keep on dividing themselves into smaller and smaller particles

 In the 1 st and 2 nd we saw the particles of sugar, salt or potassium permanganate got evenly distributed in water. Similarly, when we make tea, coffee or lemonade, particles of one type of matter get into the spaces between particles of the other. This shows that there is enough space between particles of matter.

 When we light an intense stick in one corner of room, fragrance spread in the whole room quickly. The burning of the incense stick produces gas having pleasant smell. The particles of gases produced by the burning of incense stick move rapidly in all directions, mix with the moving particles of air in the room and reach every part of the room quickly. When the gaseous particles from the incense stick reach our nose with air, we can smell the fragrance. So, the observation that the fragrance of a burning incense stick spreads in the entire room very quickly tells us that the particles of matter are constantly moving.

 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. The force of attraction or cohesion is different in the particles of matter this will become more clear from the following example

 We can move our hand in the air very, very easily because the force of attraction between the particles of air is very, very small. It is negligible.  We can also move our hand through water in a bucket fairly easily because the force of attraction between the particles of water is also small.  But we cannot move our hand through a plank of wood because the force of attraction between the particles of wood is very strong

 Rigid it means “unbending” and “inflexible” examples :- rock, wood, glass and so on.  Fluid it means “a material which can flow easily and requires a vessel to keep it examples :- milk, water, CNG, LPG and so on.

 Solids have a fixed shape and fixed volume.  They cannot be compressed much.  They have high densities.  They are heavy.  They do not fill their filter completely.  They do not flow.

 Liquids have a fixed volume but they have no shape. Liquids take the shape of the vessel in which they are kept.  Like solids, liquids cannot be compressed much.  They have moderate to high densities. They are usually less dense than solids.  They do not fill their container completely.  They generally flow easily.

 Gases have neither fixed shape nor fixed volume. Gases acquire the shape and volume of the vessel in which they are kept.  They can be compressed easily.  They have very densities. They are very, very light.  Gases fill there container completely.  Gases flow easily.

 In solids, particles are closely packed there is a force of attraction between the particles of solids which holds them, together in a fixed position.  Thus, the position of particles in a solid are fixed. The particles of solids only vibrate about their fixed position they cannot move from one position from other.  If a solid is heated, its particles starts to vibrate faster. The spaces between the particles of solid are very, very small.  The particles of a solid have minimum kinetic energy. Due to this, solids have the most orderly arrangement of particles.

 In liquids the particles are close together, but they are not as close as in solids. In fact, the particles are loosely packed in liquids.  The spaces between the particles of liquids are slightly more than that in a solid but they are still very small.  There is a quite strong force of attraction between the particles of liquids which holds them together but the force is not strong enough to hold the particles in a fixed position.

 The particles of liquids can move from on position from another within the liquid the particles of liquid have move kinetic energy than the particles of solids.  The particles in a liquid are also vibrating. Iuf a liquid is heated, then its particles begin to move faster.  Due to this, the liquids have a more disorderly arrangement of particles than solids.

 In gases the particles are much farther apart from one and another as compared to solids and liquids.  The spaces between the particles of gas are very large.  The force of attraction is negligible in particles of gas.  The position of particles of gas as well as the space between the particles of gas are not fixed.

 The particles of gas have the maximum kinetic energy.  Due to this, gases have most disorderly arrangement of particles.

 The spreading out and mixing of a substance due to the motion of its particles is called diffusion. Diffusion is one substance to another substance goes on until a uniformed mixture is formed.

 Diffusion in gases is very fast. This is because of the particles in gases move very quickly in all direction. The rate of diffusion of a gas, however, depends on its density. Light gases diffuses faster than heavy gases.

 Diffusion in liquids is slower than that gases. This is because the particles of liquids move slowly as compared to the particles of gases.

 Diffusion can also take place in solids. Diffusion is very, very slow in solids. E.g. :- When we write something on black board and leave it uncleaned for 10 or 15 days, we will find that it will become quite different difficult to clean the board afterwards. This is due to the fact that some of the particles of chalk have diffused into the surface of blackboard.

 By increasing the temp. (heating), a solid can change into liquid ; and liquid can change into gas and by decreasing gas temp. (cooling) a gas can change into liquid ; and liquid can change into solid. The point will become more clear from the following discussion.

 The process in which a solid substance changes into a liquid on heating is called melting.

 The process in which liquid substance changes into gas rapidly on heating, is called boiling.

 The process of changing gas to liquid by cooling is called condensation.

 The process of changing a liquid into solid by cooling is called freezing.

 The heat energy which has to supplied to change the state of a substance is called its latent heat. The latent heat does not in crease the temp, but latent heat has always to be supplied to change the state of a substance.  Latent heat is of 2 type:- 1) Latent heat of fusion. 2) Latent heat of vaporization.

 The latent heat of fusion9of a solid is a quantity of heat in joules required to convert 1kg of the solid to liquid, withuot any change of temperature.

 The latent heat of vaporization of a liquid is the quantity of heat in joules required to convert 1 kilogram of the liquid to vapour or gas, without any change in temperature.

 The changing of solid directly into vapours on heating, and of vapours into solid on cooling, is known as sublimation. The solid substance which undergoes sublimation is said to be “sublime”. The solid obtain by cooling the vapours of solid is called a “sublimate”.

 The process of a liquid changing into vapour or gas even below its boiling point is know as evaporation

1) temperature. 2) surface area. 3) Humidity. 4) Wind speed.

 The rate of evaporation increases on increasing the temperature of liquid.

 The rate of evaporation increases on increasing the surface of the liquid.

 When the humidity of air is low, then then rate of evaporation is high and he evaporates more readily, and when the hu, then the rate of humidity is low, and the water evaporates very slowly.

 The rate of evaporation of a liquid increases with increasing wind speed.

1) The process which takes place after evaporation. 2) Thermometer is used to measure it. 3) Anything that requires space and has mass. 4) Process that changes water to vapours. 5) Unbending and inflexible. 6) It representing the amount of water vapor in the atmosphere. 7) Spreading of something widely. 8) It fixed volume but they have no shape. 9) It can be compressed easily. 10) It cannot be compressed.