jyoti chemistry igcse revision notes

7/25/2019 JYOTI Chemistry IGCSE Revision Notes

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Chemistry IGCSE Revision Notes

Chapter 1 The Particulate Nature of Mattero Describe the states of matter and explain their inter conversion in terms of the kinetic

particle theory

Matter

o Anything that has mass and occupies space (has volume)

o Matter is composed of particles (molecules, ions, atoms)

o Spaced apart and seen with scanning electron microscope

o Are in constant motion attracting one another with inter-particle

forces (or cohesive)o Strength of inter particle force and space between particles

determines stateo

Universe

matter or energy

Scientists have developed a model called the kinetic theory, which explainsthe behavior of matter and their physical properties.

Kinetic means movement, and so kinetic energy means movementenergy.

The Kinetic Theory of Matter States:

Matter is made up of very small particles that are in constant motion. ach matter has a di!erent type of particles with di!erent si"e and

mass. #articles are in continuous movement. All particles are moving

all the time in random directions ($rownian motion).

%he speed of movement depends on the mass of the particle,

temperature and several other factors that you will know later on.

%he higher the temperature, the faster they move (more energy)- the

higher the average energy of the particles.

&eavier particles move more slowly than lighter particles at the sametemperature.

%emperature increase weakens inter-particle forces, particles spread

apart and increase in volume'si"e (i.e. pansion)

%he particles also attract each other when close, but these attractions

are weakened when the particles are far apart.

ases have greatest average energy

Solids have smallest average energy


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Average energy is measure of temperature

%here are * states of matter+ Solids, Liquids, and Gases

Physical

State

Solid

Example: Ice

Liquid

Example: Water

Gas

Example: Water vapour

Particles

Arrangement Very closely

packed and

regularly arranged

in lattice

Closely packed

and irregular

arrangement /

pattern

Very far apart and have a

very irregular or random

arrangement or say are

idely spaced

in random order

Intermolecular

Spaces

!lmost none

"egligi#le

$inimal %iny

spaces

Very large

Intermolecular

Forces

Strong forces of

attraction #eteen

particles

Weaker or less

strong attractive

forces than solids

!lmost no intermolecular

forces

&"on' existent(


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Movement of

Particles

Particles vi#rate to

and fro) #ut not

move apart and

can*t change

position therefore

have fixed volume

and shape+,Vibrate around

a fixed point-

Particles move

around and slide

past each other.

that is hy a liuid

can #e poured+

Particles move freely)

collide ith each other an

#ounce aay again &in all

the directions(. that is hy

a gas spreads+

Shape 0ixed definite

shape

"o fixed shape

1epends on the

container

"o fixed/ definite shape '

depends on the container

Volume

Increase involume-

expansion

Decrease in

volume-

contraction

0ixed Volume.

#ecause the

particles can*tmove closer) so

the volume does

not change+

0ixed Volume.

#ecause the

particles can*tmove closer) so the

volume does not

change+

"o fixed volume 2 expand

to fill the container as the

particles can move a lotcloser) so the gas can #e

pushed into a much

smaller volume+

Density 3igh $oderate to high 4o

ompressi!ility Cannot #e

compressed

Can #e hardly

compressed

Very compressi#le.

#ecause particles are far

apart and can #e pushed

together

Fluidity 1oes not flo 5enerally flos

easily

0los easily

Diffusion Cannot diffuse 1iffuses sloly 1iffuses uickly

6664iuids and gases are called fluids+

Sum up:

Solids:%he particles are packed closely together. %he forces between particles arestrong enough so that the particles cannot move freely but can only vibrate.


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As a result, a solid has a stable, denite shape, and a denite volume. Solidscan only change their shape by force, as when broken or cut.

Liquids:A liuid is a nearly incompressible uid which is able to conform to the shapeof its container but retains a (nearly) constant volume independent ofpressure.

Gases:A gas is a compressible uid. /ot only will a gas conform to the shape of itscontainer but it will also epand to ll the container.0n a gas, the molecules have enough kinetic energy so that the e!ect of forceis small, and the typical distance between neighboring molecules is muchgreater than the molecular si"e.

A gas has no denite shape or volume, but occupies the entire container inwhich it is conned.

%hese also show di!erences in how they respond to a change of pressure ortemperature+

enerally, all show an increase in volume when the temperature is increase.%hey decrease in volume when their temperatures are lowered.$ut they have di!erent !a"nitudesof epansion+

Gases #!ount of e$pansion

%NC&'#S'S (P)#&*S

Liquids

Solids

%he kinetic theory eplanation of thermal epansion+When, for example, a steel bar is heated, its particles speed up. Theyvibrate more and more, taking more space. As they do, they take up morespace, so the bar expands in all directions slightly. If the temperature falls,the reverse happens.1

%hey also show di+erences intheir responds to pressure chan"es+


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%he volume of the gasat a ed temperature can be easily reduced byincreasing the pressure on the gas. %his is because the intermolecular spacebetween the particles is huge, and so the particles can be easily broughttogether by decreasing the si"e of their container (applying pressure).i!uidson the other hand can only be slightly compressed, because theyhave very small intermolecular spaces between the particles."olid#s volumes are una!ected by changing atmospheric pressure on them.

Physical hanges "hange in State#$

#hysical changes are changes in which no new substance is formed. 2oreample melting and ice cube or dissolving salt in water. #hysical changesare reversible. 2or instance if you heat and melt and ice cube to water, youcan put it in a free"er and have it changed back to ice.3hanging the state of a matter is a physical change. And it is done by eitherheating or cooling. %he following diagram represents changes in state+

Meltin": 0t is the change of state from a solid to liuid. %he temperature atwhich a solid turns to a liuid is called the melting point. 0mpurities in thesolid'liuid can decrease the melting point.


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ree-in" or solidi.cation: 0tis the change of liuid into a solid. %hetemperature at which a liuid turns into a solid is called the free"ing point.

%hese both happen at a particular temperature called the melting'free"ingpoint. %he melting and free"ing point of any given substance are both thesame temperature such as, the melting and free"ing of pure water takesplace at 4o3.

/oilin":ventually, at a certain temperature, it becomes hot enough forgas to form within the liuid and not 5ust at the surface. $ubbles of gasappear inside the liuid. %his process is known as boiling. 0t takes place at aspecic temperature called a boiling point. 0t is the rapid change of a liuidinto a gas at a certain temperature. %he boiling point of a substance

decreases if the pressure decreases. 0mpurities in the liuid can increase theboiling point.

'0aporation or 0apori-ation:%he change of state from liuid to gas iscalled evaporation. %he temperature at which a liuid evaporates is calledthe boiling point.0f a liuid is left with its surface eposed to the air, it evaporates. %his factstates that evaporation process takes place from the surface of the liuid.

%he larger the surface area, the faster the liuid evaporates. 2urther, the

warmer the liuid is, the faster it evaporates.

"um up of both above$

'0aporation and oilin"+ evaporation constantly occurs on the surface ofliuids. %he high energy particles escape from the liuid, even at lowtemperatures. $oiling occurs at the boiling point and then the liuidevaporates everywhere in the liuid (not 5ust on the surface) and is muchfaster. 6uring a change of state the temperature of the miture does notchange.

Condensation: 0tis the change of the physical state of matter from gasphase into liuid phase. 0t can also be dened as the change in the state ofwater vapor to liuid water when in contact with any surface.

vaporation and condensation take place over (or happen on) a range oftemperatures whereas, a boiling point takes place at a specic temperature.

"um up of above one$

Any pre s!stance a"#ays me"ts and !oi"s at one partic"ar or


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Condensation and solidi.cation+ condensation is when a gas turns backinto a liuid. 7hen a gas is cooled, the particles lose energy. %hey movemore and more slowly. 7hen they bump in to each other, they do not haveenough energy to bounce away again. %hey stay close together, and a liuidforms. 7hen a liuid cools, the particles slow down even more. ventuallythey stop moving ecept for vibrations and solid forms.

Suli!ation:Some substances never eist in a liuid form. 0f they are solid and you heatthem they turn into a gas, and if they are a gas and you cool them they turninto a solid. 0n other words, substances that turns from solid to gaseousstate or from gaseous state to solid state, without changing into a liuid.

%his process is called "ublimation.A few solids like carbon dioide (8dry ice9) and iodine do not melt whenheated, but change directly into a gas. %his also happens at a specictemperature.

%he change in state occurs when the temperature is raised or dropped.Melting occurs when you heat a solid because heating gives the particlesmore kinetic energy making them move faster and further apart, makingthe solid epand. :ntil at some point they have enough energy to break theforces of attraction between them and the lattice turning into liuid. 0f youkeep heating the liuid, particles will gain even more kinetic energy andstart moving even faster, pushing each other away. %he particles at thesurface have the highest amount of energy that they can break the forces ofattraction and escape as a gas; this is the start of evaporation. At some

point, particles will try to escape so uickly that they form bubbles of gas inthe liuid. %his is the boiling point at which the pressure of the gas formingabove the liuid is the same as atmospheric pressure.


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%he following gure is a heating curve of a solid. At point 8A9 the state issolid. At point 8$9 the solid is melting; it is a miture of solid and liuid. Atpoint 839 the state is liuid. At point 869 the liuid is evaporating, it is a

&eating the liuid will cause particles to take in heat energy. So they movearound and as the particles will gain even more kinetic energy and startmoving even faster, pushing each other away. Some particles gain enoughenergy to overcome the forces of attraction between them, and escape as agas. %his is evaporation. 2urther, when at a certain point, all the remainingparticles gain enough energy to escape. %he liuid boils to a gas.

the particles move very fast and separate from each other > theliuid boils.

6uring the process of !eltin"and oilin" the temperature remain constantbecause the energy is used to break the bonds between the particles.

2n the other hand, coolin" a "as 3ill !a4e its particles lose their4inetic ener"yand move closer and slower. ventually the forces ofattraction will hold them together forming a liuid (condensation). And if a


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miture of liuid and gas. At point 89 the state is gas. %emperature 8?9 is themelting point while temperature 8@9 is the boiling point.

Heating curve

%he following gure is a cooling curve of a gas. At point 8A9 the state is gas.At point 8$9 the gas is condensing; the state is a miture of gas and liuid. Atpoint 839 the state is liuid. At point 869 the liuid is free"ing, the state is amiture of liuid and solid. At point 89 the state is solid. %emperature 8?9 isthe melting point and temperature 8@9 is the boiling point.

Cooling Curve

Some liuids evaporate etremely uickly at room temperature, they aresaid to be volatile li!uids.


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Pure and i!pure sustances:

A pure substance consists of one substance only. %here is nothing else in it >it has no contaminating impurities. A pure substance melts and boils atdenite temperatures.The purity of sustances can e easily deter!ined y testin" itsoilin" and !eltin" pointsThis is because pure substances have sharpboiling and melting points, while those of impure substances are ranging.

%he values for the melting point and boiling point of a pure substance canbe used to test the purity of a sample plus, can also be used to check theidentity of an unknown substance.

A substance9s melting and boiling points in relation to room temperature(taken as 4o3) determine whether it is usually seen as a solid, a liuid or agas. 2or eample, if the m.p. is below 4o3 and the b.p. is above 4o3, thesubstance will be liuid at room temperature.

Sustanc

e

Physical

state at

roo!

te!peratu

re

Meltin"

point5 oC

/oilin"

Point5 oC

Co!!ent: 6)789

oygen gas -BC -BD* 0f m.p. and b.p. both are

in minus sign then

denitely the substance

is a gas.thanol

(alcohol)

liuid -BBE ED 0f from m.p. and b.p

anyone has a minus

sign then it will be

liuid.7ater liuid 4

( 4F4o3

)

B44

( B44F4o3

)

0f both the values are

positive then check if

the m.p. is below 4o3

and b.p. is above 4o3,if it is so then it is a

liuid.Sodium

chloride

(common

salt)

solid D4B BGHI 0f all the above

conditions fail then,

undeniably the

substance is a solid.


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An impure substance (that has impurities in it) like sea water has salts andother impurities dissolved in it. %his make the sea water have a lowermelting point and a higher boiling point.

0n other words, the impurity can also reduce the 8sharpness9 of the meltingor boiling point. An impure substance sometimes melts or boils over a range

of temperatures, not at a particular point.

%he presence of an impurity in a substance+

Lo3ersthe melting point, and

&aisesthe boiling point of the substance

7hen a solid is melted, or a liuid is boiled, the temperature stays constantuntil the process isco!plete. %he same is true in reverse when a gascondenses or a liuid free"es.

Describe and explain diffusion.

%he process by which particles mi and spread, through random

collisions with other particles, is called di!usion.

0t is basically the movement by which substances disperse themselves

spontaneously.

%wo gases eventually become mied when they are mied

%he movement of particles of uid from a region of higher

concentration to a region of lower concentration in order to maintain aconstant concentration in the given space.

#articles travel in random "ig"ag motions, this is how smells spread,

solids dissolve, and dust particles travel in a random way when

suspended in air.

/ro3nian Motion: the apparent random movement of small particles.

6i!usion is a random process. So, the path a particle takes depends on

its collisions.

6i!usion does not take place in solids.

6i!usion in liuids is much slower than in gases.

6i!usion in liuids is also called dissolving.

0t is much faster in gases than in liuids because particles move much

faster in gases. So they collide with more force, and have space to

bounce further away.

As the temperature rises, particles take in energy and move faster. So

di!usion is faster too.


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Describe evidence for the movement of particles in gases and liquids (a treatment of

Brownian motion is not required)

Some evidence for particles+%emonstrating %i&usion in i!uids$

7hen a potassium permanganate crystal is suspended at the bottom

of a beaker, J lled with water, the permanganate crystals will tend todisperse themselves evenly throughout the beaker. After hours, apurple solution of the same shade was observed.

planation+ 7hen you drop a crystal of purple potassium manganate

(K00) into water, the purple colour spreads through the water. %his is

because- the particles leave the crystal. %hey collide with movingwater particles and bounce away again. 0n this way, they mi andspread all through the liuid.

#recautions+-

6o not stir or shake the miture in anyway that may aid it to mi#rovide a short distance for di!usion, in other words do not over ll thebeaker, prolonging the time taken for distribution.

periment could also be done through 3opper (00) Sulphate crystals inwater+

A copper sulphate crystal is put in water beaker. 0t is then left to stand. Atrst the water net to the crystal becomes blue as the solid dissolves.#articles move o! the surface of the crystal. ventually the crystal dissolvescompletely and the whole solution becomes blue. %he particles of thecrystal have spread out evenly in the liuid.


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6emonstrating 6i!usion in as+

A 5ar of dense green gas, chlorine, is put

underneath a 5ar of air

$ecause gases consist of fast-moving

particles, when the 5ars are eposed toeach other, molecules of air and chlorinespread themselves between the two 5ars

7ith time, both gas 5ars consist of green

gas of uniform intensity

Also, an aerosol spray can be released at

the front of a room, with time theoccupants at the back of the room cansmell the spray because the gas movedgradually to the back of the room.

"ome gas 'ar experiment could also be done with bromine$

A gas 5ar of air and a gas 5ar of bromine are connected; the bromine

travels up the tube.

6i!usion of gases can be proved very easily. 7e can prove it by putting

some bromine liuid in a cylinder and sealing it, then putting anotherinverted cylinder above it. 7hen the bromine liuid evaporates, weremove the lid between the two cylinders; the brown bromine gas willdi!use upwards lling the available space.

Coo4in" s!ell spreads:

o %he smell of cooking can travel from the kitchen all through the house.

o planation+ A 8smell9 is due to gas particles from the food. %hey collide

with the gas particles in air, and bounce away again. 0n this way, they

spread everywhere. @ou smell them when they reach your nose.

Describe dependence of rate of diffusion on molecular mass (treated qualitatively)

Factors that affects the rate of diffusion:

%ass o& the s!stance'

%he lighter the substance (lower Mr or Ar) the faster it di!uses.


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ases with larger molecules have higher densities than gases which

have small molecules. .g. 3hlorine molecules are *I.I larger than

hydrogen molecules and chlorine is denser than hydrogen.

&eavier particles move more slowly than lighter particles at the same

temperature; larger molecules di!use more slowly than smaller

(lighter) ones. And we can also say that, dense gases di!use more

slowly than gases of low density. %hus, the rate of di!usion depends on the molecular mass'density of

gas.

(ate of di&usion is inversely proportional to mass.

Particle !ass decreases rate of di+usion increases and 0ice

0ersa(this is shown by the following eperiment).

(emperatre'

%he higher the temperature, the faster a gas will di!use. $ecause particles gain energy as they are heated.

So, the more kinetic energy the particles have, the faster they move

and di!use.

)or example- 7hen #otassium #ermanganate (LMn


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*ote$

%he pressure of gas is the result of collisions of the fast - moving

particles with the walls of the container.

Comparing the rates of diffusion for gases:

ven at the same temperature, gases do not di!use at the same rate. ookat this eperiment.

Ammonia So"tion+ /&* *ydroch"oric Acid- &3l +hite smoke o&Ammonim ch"oride- /&G3l

0f particles of ammonia gas half the mass of particles of hydrogen

chloride gas are soaked in cotton wool and placed at two ends of atube (corked on both sides) then; when these gases come in contact,white smoke of Ammonium 3hloride forms. $ecause the smoke forms

closer to the &3l, it shows that ammonia gas molecules travelledfaster in the same length of time.

#articles of ammonia gas and hydrogen chloride gas di!use from the

opposite ends of the long glass tube. (%he particles are molecules.)7hen they meet, they combine to form a white cloud of ammoniumchloride. %he white cloud forms closer to the right-hand end. So theammonia molecules have travelled faster. %hat9s because they arelighter. (%he relative molecular masses are+ ammonia+ BE; hydrogenchloride+ *H.I.)

The lo3er its relati0e !olecular !ass, the faster a "as 3illdi+use

)artic"e mass decreases rate o& di-sion increases and

vice versa this is sho#n !y the a!ove e/periment0.

/ote+ 6issolving (di!usion in liuids) can be speed up by

increasing temperature or stirring.


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jyoti chemistry igcse revision notes

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