Chapter 12 Rates of Reaction

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Chemistry:Chapter

12-Rates of Reaction

Rates of Reaction




Rates of Reaction

ffect of concentration

ffect of cata!ysts

"ntrod#ction

$#mmary acti%ities

ffect of temperat#re

Contents

ffect of s#rface area



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Rates of reactions

The speed of different chemical reactions varies hugely. Some

reactions are very fast and others are very slow.

s!ow

%ery fast

%ery s!ow

fast

s!ow

r#stin'

e(p!osion

chemica! weatherin' of rocks

sodi#m and water

rottin' fr#it

Reaction Rate

What is the rate of these reactions?

The speed of a reaction is called the rate of the reaction.




Reactions) partic!es and co!!isions

Reactions take place when particles of reactants collide with

a certain amount of energy.

This energy is called acti%ation ener'y, and is different for

each reaction.

The rate of a reaction depends on two things:

the fre*#ency of collisions between particles

the ener'y with which particles collide.

!f particles collide with less energy than the activation energy,

they will not react. The particles will "ust bounce off each

other.




!ncreased temperat#re

increased concentration of

dissolved reactants, and increased

press#re of gaseous reactants

increased s#rface area of solid

reactants

use of a cata!yst.

Chan'in' the rate of reactions

#nything that increases the number of successful collisions

between reactant particles will speed up a reaction.

What factors speed up reactions?



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,C./R$ ,,C." . R.$ /,

RC."/$

$ http:%%www.youtube.com%watch?

v&c'SfrhS##()

*lease watch this video carefully to answerthe given worksheet




nswer the fo!!owin' *#estions ased

on the %ideo

+.What are the fi%e factors that affects speed up reactions?

i.

ii.

iii.

iv.

v.

-. Which factor is only relevant for gaseous reactions?

. What are the two conditions for effective collision?

i.

ii.

/ .#ny factors that increases the rate of effective collision will also the speed of reaction.

0. Why does the speed of reaction increase at higher concentration?

1. Why does the speed of reaction increase at higher pressure?

(. Why does the speed of reaction increase when the temperature of a reaction is increased?




nswer the fo!!owin' *#estions ased

on the %ideo 6nswers7

+.What are the fi%e factors that affects speed up reactions?

i.2oncentration

ii.*ressure

iii.Temperature

iv.*article si3e

v.2atalyst

-. Which factor is only relevant for gaseous reactions?

*ressure

. What are the two conditions for effective collision?The reacting particles must collide head4on with each other 5head4on collision6

The reacting particles must collide with minimum amount of energy5activation energy6

/ .#ny factors that increases the rate of effective collision will also the speed of reaction.

0. Why does the speed of reaction increase at higher concentration?

#t higher concentration, there are more reactant particles per unit volume available to collide with each other. This increases the fre'uency of

effective collisions and thus increases the speed of reaction.

1. Why does the speed of reaction increase at higher pressure?

#t higher pressure, the particles of gaseous reactants are closer together, hence there are more particles per unit volume of gas available to

collide with each other. This increases the fre'uency of effective collisions and thus increases the speed of reaction.

(. Why does the speed of reaction increase when the temperature of a reaction is increased?

#t higher temperature, reactant particles moves faster resulting in increase in the fre'uency of effective collisions between particles. 7ikewise,

an incr ease in temperature will result in more particles having the minimum activation energy to collide increasing the speed of reaction.


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8eas#rin' rates of reaction

8easuring the rate of a reaction means measuring the

rate of chan'e over a period of time.

This can be done by measuring the:

i. change in the mass of a reactant or the

ii.change in the volume of a product



i Chan'e in the mass of reactants

Ca!ci#m

caronatehydroch!oric

acidca!ci#m

ch!orideCarondio(ide

;ater

$ What can you measure to calculate the rate of reaction

between calcium carbonate and hydrochloric acid?

The mass of reactants before, during and after the

reactions

9ote: marble chips contains calcium carbonate



ii7 Chan'e in the %o!#me of prod#cts

$ What can you measure to calculate the rate of reaction

between magnesium and hydrochloric acid?

ma'nesi#mhydroch!oric

acid

ma'nesi#m

ch!oridehydro'en

The volume of hydro'en prod#ced 5cm%min6.



$!ower and s!ower<

Reactions do not proceed at a steady state. They start off at

a certain speed, then get slower and slower until they stop.

#s the reaction progresses, the concentration of reactants

decreases. This reduces the fre'uency of collisions between

particles and so the reaction slows down.

percenta'e comp!etion of reaction

reactant #

reactant

product0=

fast

25=

s!ower

35=

%ery s!ow

100=

stopped


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Rate of reaction and 'raphs



raphs and reactant-prod#ct mi(



Rates of Reaction


ffect of cata!ysts

"ntrod#ction

$#mmary acti%ities



Contents


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.he effect of temperat#re on co!!isions

;ow does temperature affect the rate of particle collision?



.emperat#re

The higher the temperature, the faster the rate of a reaction.

!n many reactions, a rise in temperature of +<=2 causes the

rate of reaction to appro>imately double.

Why does increased temperature increase the rate of

reaction?

#t a higher temperature, particleshave more energy. This means

they move faster and are more

likely to collide with other particles.

When the particles collide, they doso with more energy, and so the

number of successful collisions

increases.



.emperat#re and food

ood goes off because chemical reactions take place.

Why does food remain usable for much longer if it is kept in

a free3er?

The low temperature in the free3er means that particles will

move much slower and with less energy than if they were atroom temperature. This means that there are fewer

successful collisions and so a slower rate of reaction.



.emperat#re and cookin'

efore microwave ovens were common, many people used

pressure cookers to cook food more 'uickly.

!n a pressure cooker, water

doesn@t boil until it reaches about

++0=2. ;ow does this help

cooking?

The higher temperature means that particles move more

'uickly and with more energy. This means that there are

more successful collisions between particles, and the food

cooks more 'uickly.



.emperat#re and rate of reaction

The reaction between sodi#m thios#!fate and hydroch!oric

acid produces s#!f#r .

Sulfur is solid and so it turns the solution cloudy.

The effect of increasing temperature on the rate of reactioncan be measured by comparing how long it takes the

solution to turn cloudy at different temperatures.

hydroch!oric

acid

sodi#m

ch!orides#!f#r

sodi#m

thios#!fate water s#!f#r

dio(ide

a2$

2/

&

5a'6

2C!

5a'6

2aC!

5a'6

$

5s6

$/2

5g6

2/

5l6



$odi#m thios#!fate and hydroch!oric acid

To run the e>periment investigating the effect of temperature

on the rate of reaction:

1 8ark a cross on a piece of paper.

2 #dd a known amount of sodium thiosulfate to a beaker,

and place it on the piece of paper.

& #dd a known amount of hydrochloric acid to the beakerand immediately start a stop4clock. The solution will begin

to turn cloudy.

4 #s soon as the cross can no longer be seen, stop the

clock and note the time.

5 Repeat the e>periment at different temperatures using the

same volume of reactants. 2ompare how long it takes the

cross to disappear.

$ di hi !f d h d h! i id



$odi#m thios#!fate and hydroch!oric acid

When looking down into the beaker, the cross will become

fainter over time:

The time taken for the cross to disappear can be used as thetime of the reaction.

http:%%www.youtube.com%watch?v&;Wvf(;AshB)

increasin' time

.i f ti t t h


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.ime of reaction %s temperat#re 'raph

. f ! >



.r#e or fa!se>

C t t



Rates of Reaction


ffect of cata!ysts

"ntrod#ction

$#mmary acti%ities



Contents

" i t ti


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"ncreasin' concentration

C t ti



Concentration

The higher the concentration of a dissolved reactant, the

faster the rate of a reaction.

Why does increased concentration increase the rate of

reaction?

#t a higher concentration, there are more particles in the

same amount of space. This means that particles are morelikely to collide with other particles.

!ow concentration hi'h concentration

C t ti d ti ! !!i i




Concentration and partic!e co!!isions

R ti t id d t !




Reactive metals such as magnesium react with acid to

produce hydrogen gas.

Reaction etween acid and meta!

hydroch!oric

acid

ma'nesi#m

ch!oridema'nesi#m hydro'en

2C! 5a'68' 5s6 8'C!2 5a'6

2 5g6

The effect of increasing concentration on the rate of reaction

can be measured by comparing how 'uickly hydrogen is

produced using different concentrations of hydrochloric acid.

8' C!: e(periment set #p



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8' C!: e(periment set-#p

What e'uipment do you need for the e>periment investigating

the effect of concentration on the rate of reaction?

ma'nesi#m

rion

r#er #n'

hydroch!oricacid

r#er

connector 'as syrin'e

'!ass

t#e

conica!

f!ask

8a'nesi#m and hydroch!oric acid




8a'nesi#m and hydroch!oric acid

To run the e>periment investigating the effect of concentration


1 8easure out a fi>ed volume of hydrochloric acid into

the conical flask.

2 #dd a known mass of magnesium to the flask, immediately

attach the gas syringe and start a stop4clock.& 8easure the volume of hydrogen collected in the syringe

at regular intervals until no more gas is produced.

4 Repeat the e>periment using a different concentration of

hydrochloric acid but using the same volume of acid and

the same mass of magnesium. 2ompare the rate at which

hydrogen is produced.

8' C!: different concentrations




8' C!: different concentrations

?ress#re



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The gas particles become closer together, increasing the

fre'uency of collisions, and so increasing the rate of reaction.

?ress#re

Why does increasing the pressure of gaseous reactants

increase the rate of reaction?

#s the pressure increases, the space in which the gas

particles are moving becomes smaller.

The samenumber of

particles but in a

smaller space.

!ow press#re hi'h press#re

ContentsContents




Rates of Reaction


ffect of cata!ysts

"ntrod#ction

$#mmary acti%ities


Contents


Contents

$#rface area




$#rface area

#ny reaction involving a solid can only take place at the

surface of the solid.

!f the solid is split into several

pieces, the surface area increases.

The smaller the pieces, the larger the surface

area. This means more collisions and a faster

rate of reaction.

This means that there is an increased area for

the non4solid reactant particles to collide with.

s!ow

rate

fast

rate

$#rface area and partic!e co!!isions



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$#rface area and partic!e co!!isions

Reaction etween a caronate and acid




Reaction etween a caronate and acid

8arble chips are made of calcium carbonate. They react with

hydrochloric acid to produce carbon dio>ide.

The effect of increasing surface area on the rate of reaction

can be measured by comparing how 'uickly the mass of thereactants decreases using marble chips of different si3es.

hydroch!oric

acid

ca!ci#m

ch!oride

ca!ci#m

caronate water caron

dio(ide

CaC/& 5a'6

2C!5a'6 CaC!2

5a'6 2/5a'6 C/2

5g6

CaC/ C!: e(periment set-#p




CaC/& C!: e(periment set-#p

What e'uipment do you need for the e>periment investigating

the effect of surface area on the rate of reaction?

cotton woo!

@p!#'A

hydroch!oric

acid

conica!

f!ask

ca!ci#m

caronate

chips

wei'hin'sca!es

Ca!ci#m caronate and hydroch!oric acid




Ca!ci#m caronate and hydroch!oric acid

To run the e>periment investigating the effect of surface area


1 8easure out a fi>ed volume of hydrochloric acid into a

conical flask and place the flask on weighing scales.

2 #dd a fi>ed mass of calcium carbonate chips to the flask,

and place a cotton wool plug in the neck. This stops the

li'uid from spitting while allowing the 2C- to escape.

& egin taking mass readings straight away, and continue

until there is no further change in mass.

4 Repeat the e>periment using the same mass of calciumcarbonate but of a smaller chip si3e, and the same

volume of hydrochloric acid. 2ompare the rate at which

the mass of reactants decreases.

CaC/ C!: different s#rface areas




CaC/& C!: different s#rface areas

Contents




Rates of Reaction


ffect of cata!ysts

"ntrod#ction

$#mmary acti%ities



Contents

;hat are cata!ysts>




;hat are cata!ysts>

What are catalysts?

Cata!ysts are s#stances that chan'e the rate ofa reaction witho#t ein' #sed #p in the reaction

2atalysts are very important in industry because products

can be made more 'uickly, saving time and money.They can also avoid having to use high temperatures, so

they can save fuel and reduce pollution.

2atalysts are also very important in living cells. iologicalcatalysts are special types of protein called enymes.

(amp!es of cata!ysts




(amp!es of cata!ysts

icke! is a catalyst in the production of margarine

5hydrogenation of vegetable oils6.

"ron is a catalyst in the production of ammonia from

nitrogen and hydrogen 5the ;aber process6.

8any catalysts are transition metals or their compounds.

Different reactions use different catalysts. or e>ample:

?!atin#m is a catalyst in the

catalytic converters of car

e>hausts. !t catalyses the

conversion of carbon mono>ide

and nitrogen o>ide into the less

polluting carbon dio>ide and

nitrogen.

ow do cata!ysts work>




ow do cata!ysts work>

;ow do catalysts work?

Different catalysts work in different ways, but most solid

catalysts work by lowering the amount of energy needed for

the reaction to take place.

or a chemical reaction to take place:

the reacting parts of particles need to be brought together.

energy is needed to break e>isting bonds, so new

bonds can be formed

Cata!ysts work y !owerin' the

acti%ation ener'y of a reaction

ow a p!atin#m cata!yst works




ow a p!atin#m cata!yst works

When hydrogen and o>ygen are mi>ed in a "ar, there is no

reaction. !f a platinum wire is added, the gases react instantly

with a loud pop, producing water.

;ow does platinum catalyse this reaction?

The gas molecules are brought

together onto the surface of theplatinum. They are adsored.

The molecules are much closer

together and their bonds are

weakened, lowering theactivation energy of the reaction.

p!atin#mwire

o(y'en

mo!ec#!e

hydro'en

mo!ec#!eThe larger the surface area

of the platinum, the 'uicker

the reaction.

ecomposition of hydro'en pero(ide



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Without a catalyst, this reaction is very slow, and can take

months. With a catalyst such as manganese 5!E6 o>ide, the

reaction takes minutes.

ecomposition of hydro'en pero(ide

;ydrogen pero>ide decomposes into water and o>ygen.

22/ 5l622/2 5a'6 /2 5g6

water hydro'enpero(ide

o(y'en

Cata!ysts ne%er prod#ce more prod#ct D they

E#st prod#ce the same amo#nt #t *#icker

Contents




Rates of Reaction


ffect of cata!ysts

"ntrod#ction

$#mmary acti%ities



Contents

!ossary




!ossary

acti%ation ener'y D The amount of energy needed for a

reaction to begin.

adsorption D The formation of a layer of molecules on the

surface of a solid.

cata!yst D # substance that changes the rate of a reaction

without being used up.

concentration D The amount of particles in a given

volume.

enyme D # biological catalyst.

rate of reaction D The speed with which a particular

chemical reaction progresses.

"ncrease or decrease>




"ncrease or decrease>

$ta'es of a reaction




$ta'es of a reaction

8#!tip!e-choice *#i



8#!tip!e choice *#i

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Chapter 12 Rates of Reaction