matter in oursurroundings-ix chemistry chapter 1

7/31/2019 Matter in Oursurroundings-ix Chemistry Chapter 1

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MATTER IN OURSURROUNDINGSMATTER:-Anything which occupies space and has mass is called Matter.E.g. Wood and metals, Water and Kerosene, Hydrogen and Oxygen

Matter is classified in many ways. Modern day scientists have classifiedmatter in two ways: On the basis of its physical properties and on thebasis of its Chemical properties.

On the basis of physical properties matter can be classified into three1. Solids, 2. Liquids and 3. Gases

On the basis of chemical properties matter can be classified into three

1. Elements 2. Compounds 3. Mixtures.

MATTER IS MADE OF PARTICLES

Every matter around us is made of tiny particles. The number of particlein a matter is very large. The particles of matter are very large even wecannot see them with high power microscope. The particles which makeup matter are constantly moving.

The particles which made up matter are Molecules or Atoms.

Characteristics of particles of matter.

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

CLASSIFICATION OF MATTER AS SOLIDS, LIQUIDS AND GASES:

Matter exists in three physical states: SOLIDS, LIQUIDS AND GASES.


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PROPERTIES OF SOLIDS:-

i. Solids have fixed shape and volumeii. Solids cannot be compressed.

iii. Solids have high densities.iv. Solids dont fill their container completely.v. Solids dont flow.vi. Solids are rigid.

PROPERTIES OF LIQUIDS:-

i. Liquids have fixed volume but they dont have fixed shape.ii. Liquids cannot be compressed much.

iii. Liquids are less dense than solids.iv. Liquids cannot fill their container completely.v. Liquids flow easily. Therefore they are called Fluids.

PROPERTIES OF GASES:-

i. Gases neither have fixed volume nor have fixed mass.ii. Gases can be compressed completely and easily.iii. Gases have very low densities.

iv. Gases fill their container completely.v. Gases flow easily, therefore they are called fluids.

In solids, the particles are closely packed. A solid has fixed shapebecause the particles of the solid are closely packed and their positionsare fixed due to the strong force of attraction between them. A solid hasfixed volume and can not be compressed because the spaces between itsparticles are fixed. A solid can not fill the container completely and

cannot flow because its particles are closely packed.A rubber band changes its shape but we still call it a solid because itchanges its shape by the action of force and when the force is removedthe rubber band regains its shape.


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If salt and sugar not appear to have fixed shape but we still count themin solids because the shape of the individual crystals is considered to besolid because the shape of individual crystals is fixed.

A sponge can be compressed easily but still we count them in solidsbecause they have minute pores in it which are filled with air. When wepress the sponge air is expelled from its holes making it highlycompressible. A solid cannot be compressed by either applying thepressure or by changing the temperature.

In the liquids the particles are close together but they are not as close assolids. Spaces between particles in liquids are slightly more than in solids.

There is weaker force of attraction between the particles of liquids thanin solids. They dont have fixed shape because the positions of itsparticles are not fixed due to comparatively less strong force of attractionbetween them. A liquid has fixed volume because at the giventemperature, the spaces between its particles are fixed. A liquid can notbe compressed much because they have less space between the particlesof them. A liquid generally flows easily because its particles are able toslide over another due to slightly weaker inter particle forces ofattraction. A liquid cannot be compressed by applying the pressure it can

be compressed by changing the temperature.

In gases the particles are much farther apart from one another ascompared to solids and liquids. The spaces between the particles ofgases are very large. The force of attraction between the particles ofliquids is negligible. Particles of gas are free to move in any direction.

A gas has not fixed shape because the position of its particles is not

fixed. A gas can be compressed easily because its particles are far apartfrom each other, there are large spaces between them. A gas can fill thecontainer completely because due to the high kinetic energy andnegligible forces of attraction, the particles of gas move with high speedin all direction. A gas can flow easily because its particles are free tomove anywhere. Gas can be compressed by applying the pressure.


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PROBLEMS FOR PRACTICE1. State characteristic properties of each solids, liquids and gases.2. Give reasons for saying wood is a solid.3. Why does a gas exert pressure?

4. Why are gases highly compressible whereas solids and liquids cannotbe compressed?5. Why do gases have neither a fixed shape nor a fixed volume?6. What is general name of :i.Rigid form of matter?ii.Fluid form of matter.7. 1.Name two gases which are supplied in compressed form in homesand hospitals.2.Write the full form of CNG and LPG.3.Give two reasons tojustify:i.Water is a liquid at room temperature?ii.An iron almirah is solid.

The spreading out and mixing of a substance with another substance dueto the motion of its particles is called diffusion. Diffusion goes on untiluniform mixing is formed. Diffusion occurs an solids, liquids and in gases.Fastest in gases and slowest in solids and moderate in liquids.Phenomena of diffusion tell us that the particles are constantly moving.

DIFFUSION IN GASESThe diffusion in gases is fastest than solids and liquids. EXAMPLES

The smell of food being cooked reaches us even from considerabledistance because when food is cooked the some of the substancesrelease gases having the smell of food in them. The particles of gasesmove very quickly and mix up with the air by diffusion. When the aircontaining these gases reaches our nose we get the smell of food beingcooked.

The fragrance of burning incense stick spreads all around due to thediffusion of its smoke in air. The particle of gas produced by the gases of

incense stick move rapidly in all directions. They collide with the particlesof air present in the room; mix with air and reach every part of the room.The smell of perfumes spread due to diffusion of perfumes vapour intothe air. When the bottle of perfume is opened, then the liquid perfumequickly changes into vapours. The perfume vapours move very rapidly inall directions in air and mix with the air particles and hence spread withair particles. LPG in our homes is detected due to the diffusion of a


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strong smelling substance (ethylmercaptan) present in the cooking gas,into air.

Matter can exist in three physical states; solids, liquids and gaseousstate. Two factors which decide whether a given substance would besolid, liquid or gas is; Temperature and Pressure.

EFFECT OF CHANGE OF TEMPERATUREBy increasing the temperature a solid can be converted into liquid state;and a liquid can be converted into gaseous state, and by decreasing thetemperature a gas can be converted into liquid state; a liquid can beconverted into solid state.

1. SOLID TO LIQUID CHANGE: MELTING or FUSIONThe process in which a solid substance is converted into liquid on heatingis called Melting. The temperature at which a solid substance changesinto liquid is called melting point. For example the ice melts at thetemperature of o0C to form liquid hence o0C is the melting point of ice.

2. LIQUID TO GAS: BOILING OR VAPOURISATIONThe process in which a liquid changes into a gas on heating, is called

boiling or vapourization. The temperature at which a liquid boils andchanges into a gas atmospheric pressure is called boiling point of theliquid. For example the boiling point of water is 100oC.

3. GAS TO LIQUID: CONDENSATIONThe process of changing a gas to a liquid by cooling is calledcondensation. Condensation is reverse of boiling. For example whensteam changes into water by cooling it is called condensation.

4. LIQUID TO SOLID CHANGE: FREEZINGThe process of changing a liquid into a solid by cooling is called freezing.Freezing means solidification. Freezing is reverse of melting. For examplewater freezes to form ice.


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5. SUBLIMATION:The changing up of solid into vapours on heating and of vapours intosolid on cooling is known as Sublimation. The substances which undergosublimation are ammonium chloride, iodine, camphor, naphthalene, and

anthracene.

LATENT HEATThe heat energy which has to be supplied to change the state of asubstance. Latent heat does not change the temperature of a substance.It only changes the state of a substance. It is called latent heat becauseit becomes hidden in the substance undergoing the change of state, anddoes not show its presence by raising temperature. So latent heat cannotbe detected by thermometer.

Why latent heat does not cause a rise in temperature of a substance?

The latent heat which we supply is used up in overcoming the force ofattraction between the particles of a substance during the change ofstate. Latent heat does not increase the kinetic energy of the particles ofthe substance. And since there is no change in kinetic energy of theparticles the temperature of a substance does not rise during the changein 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 latent heat of fusion (melting) in a solid is the quantity of heat injoules required to convert 1 kilogram of the solid to liquid without anychange in temperature. The latent heat of fusion of ice is 3.3410>5joules per kilogram. The amount of heat required to convert a unit mass of a solid at its melting

point into a liquid without an increase in temperature. Liquids release the same amount of heat when theysolidify. "the heat of fusion is equal to the heat of solidification"

Why the temperature of melting ice does not rise even though heat isbeing supplied continuously?

In this process heat energy is used up in changing the state of solidsubstance by overcoming the force of attraction between its particles. Soamount of particles in water at o0C have more energy as compared to


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particles in ice at the same temperature. Ice at o0C is more effective incooling a substance than water at the same temperature.

LATENT HEAT OF VAPOURISATION (LIQUID TO GAS CHANGE)

The latent heat of vaporization is the quantity of heat in joules requiredto convert 1kilogram of liquid to vapor or gas without any change intemperature. The latent heat of vaporization of water is 22.510>5joules per kilogram.

Why the temperature of boiling water does not raise even though heatingis given continuously?

The heat energy supplied to a boiling liquid is used up in changing the

state of the liquid substance by overcoming the force of attractionbetween its particles.

Why the burns caused by steam are much more severe than thosecaused by boiling water though both of them are at the sametemperature?

This is due to the fact that steam contains more heat in the form oflatent heat than boiling water.

EFFECT OF CHANGE OF PRESSUREThe physical state of mater can also be changed by changing thepressure. Gas can be changed into liquids by increasing the pressureaccompanied by lowering the temperature. And some solids like solidcarbon dioxide can change into gases on decreasing the pressure. Thereis a lot of space in between the particles of gas. We can reduce thespaces between the particles of a gas by enclosing it in a cylinder andcompressing it by pushing in the piston. If enough force is applied by thepiston the gas is highly compressed. The particles of the gas get so closetogether that they start attracting each other to form liquid. Ammoniagas can be liquefied by applying the pressure and lowering temperature.

Solid carbon dioxide is stored under high pressure?

This is because decreasing the pressure on solid co2


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it gets converted directly into gas CO2. Solid CO2is extremely cold substance. It is used to deep freeze food and to keepice creams.

EVAPORATIONThe process of changing up a liquid into vapour or gas even below itsboiling point is called Evaporation. Whatever be the temperature at whichevaporation takes place the latent heat of vaporization must be suppliedwhenever a liquid changes into a vapor or gas.

CAUSE OF EVAPORATIONSome particles in liquid always have more kinetic energy than others. Soeven when a liquid is below its boiling point, some of its particles have

enough energy to break the force of attraction between the particles andescape from the surface of the liquid in the form of vapor.

FACTORS AFFECTING EVAPORATION1.TEMPERATUREThe rate of evaporation increases on increasing the temperature of theliquid. An increase of temperature: With the increase of temperature,more number of particles get enough kinetic energy to go into the vaporstate.

2. SURFACE AREA OF LIQUID.an increase of surface area: We know that evaporation is a surfacephenomenon. If the surface area is increased, the rate of evaporationincreases. For example, while putting clothes for drying up we spreadthem out.3. HUMIDITY OF AIRHumidity is the amount of water vapour present in air. The air around uscannot hold more than a definite amount of water vapour at a given

temperature. If the amount of water in air is already high, the rate ofevaporation decreases.4.WIND SPEED an increase in wind speed: It is a common observation that clothes dryfaster on a windy day. With the increase in wind speed, the particles ofwater vapour move away with the wind, decreasing the amount of watervapour in the surrounding.


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What is the cause of cooling caused by evaporation?When a liquid evaporates it draws the latent heat of vaporization fromanything which it touches. By losing heat the substance gets cooled.1.If

we put A little of spirit or patrol at the back of our hand and wave itaround the spirit evaporates rapidly and our hands feels very cold. This isdue to the fact that to change from liquid to gas state spirit requireslatent heat of vaporization which spirit takes by our hand. Our handlooses heat and gets cooled.2.During hot summer days water is usually kept in earthen pots to keep itcool. The earthen pot has a large number of pores in its walls. Some ofwater continuously seeps out through these pores. This water evaporate

and continuously and takes the latent heat of vaporization from thesurface of the pot and remaining water. In this way remaining waterlooses heat and becomes cool.3.Respiration or sweating is our bodys method of maintain constanttemperature. On a hot day or after doing some physical exercise. Whenour body temperature tends to rise too much our sweat glands give outmoisture on our skin. When the sweat evaporates it takes the latent heatof vaporization from our body. This keeps our body cool.

matter in oursurroundings-ix chemistry chapter 1

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