Chapter 1 Form 5 Chemistry 2015

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1.1 RATE OF REACTION

Definition

Speed at which reactants are converted into

products in a chemical reaction.

Examples of fast/slow reactions.

Type of rxn Fast rxn Slow rxLiberation of

gasCarbonate compound + dilute HCl

Na2CO + 2HCl 2NaCl + CO2 + H2O!"otos#nt

$CO2 + $H2O C

!recipitation &gNO + NaCl &gCl + NaNO Na2'2O + 2HCl 2N

H2O

Heating metal

in air

Heating of potassium

() + O2 2)2O

Heating of

2Cu + O2


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Fast reacton!

t"e ta#en s s$ort

So% t$e reactants s &'c#ly con(erte)

pro)'cts.

T$'s% t$e rate of reacton s $+$.


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Meas'rn+ t$e Rate of Reacton

Changes in selected quantity Rate of reaction = _______________________________________________

Time taken

'uitable c"anges*•

-olume of gas liberated• precipitate formation• c"ange in mass during t"e reaction• colour c"anges• temperature c"anges•

pressure c"anges


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A(era+e rate of reacton

The average value of the rate of reaction withi

specified period of time.

Average rate of reaction =Changes in selected quan _____________________________________

Time taken

Notes:

Reaction with high ROR, completed in short time.

Reaction with low ROR, completed in longer time.


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1. FACTORS AFFECTIN/ THE RATE OF REA

,$y t$ese two c'r(es )fferent0

a) Total surface are

of solid reactant

b) Concentration o

c) Temperature of r

d)Use of catalyst

e) Pressure of gaseo


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1. CO22ISION THEOR3

To better understand of collision theory you must knothings related to the theory which is;

• C$e"cal e&'aton• Collson•

Effect(e collson• Act(aton ener+y• Collson fre&'ency• Effect(e collson fre&'ency• Ener+y profle )a+ra"


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,$at s t$e Collson T$eory0

During a reaction t"e partcles oreactants must coll)e wit" eac" ot"er fo4rea#n+ and t"en 4on) for"aton to opro)'ce pro)'ct.

Bond breaking : absorb heat energy

Bond formation : release heat energy


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,$at s t$e Collson T$eory0

"ose collisions w"ic" ac"ie-ed a "act(aton ener+y and wit" t"e corentaton will result in a reacton.collisions are called effect(e collsons.

0f t"e particles collide wit" less energacti-ation energ# or wit" wrong orienta

will not result in reaction is called nefcollsons.


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Effect(e Collsons

T$ose collsons w$c$ ac$e(e) a "n"'

act(aton ener+y Ea6 an) wt$ t$e correcorentaton% wll res'lt n a reacton.

Act(aton Ener+y

Act(aton ener+y s t$e ener+y 4arrer t$"'st 4e o(erco"e 4y t$e coll)n+ partclet$e reactants n or)er for reacton to occ'


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a6 Effect of S'rface Area-S7e on t$e ROR

SMA22ER s7e sol) reactant

8++er total s'rface area per (ol'"e

H+$er fre&'ency of effect(e collson

H+$er rate of reacton

8I//ER s7e sol) reactant

• S"aller total s'rface area per (ol'"e

• 2ower fre&'ency of effect(e collson

• 2ower rate of reacton


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1olume of gas -s time grap"

rap" 0 is more steeper t"

"us t"e gradient of grapgrap" 00

"us t"e rate of reactionis "ig"er t"an experimen

I : Small marble

II : Large marble

Volume of

gas / cm3

Time / min

I II

V

t

t!

Question: Why the total o

same"

ns!er: The number of m

is same


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a6 Effect of S'rface Area-S7e on t$e ROR

"e total s'rface area per (ol'"e expose) to collision wit" ot"er reactant 3namparticles is 4++er.

"us t"e number of collision among t"e reacting particles at t"e surface of t"e

increases. fre&'ency of collsson is $+$er.

"us t"e number of collision ac"ie-ed t"e acti-ation energ# to become effecti-e

increases.

"is lead to an ncrease in t"e fre&'ency of effect(e collson. Hence a $+$er rate of reacton.

"en t"e s7e of fixed mass of solid reactant 3ex5 CaCO4 is


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46 Effect of Concentraton on ROR

"en t"e concentraton of t"e solution of a reactant ncreases*

• "e n'"4er of partcles per 'nt (ol'"e of t"e solution of t"e

ncreases.

• "us t"e number of collision among t"e reacting particle

Fre&'ency of collsson is $+$er.

• "us t"e number of collision ac"ie-ed t"e acti-ation energ

effecti-e collision is also increases.

• "is lead to an ncrease in t"e fre&'ency of effect(e collson.

• Hence a $+$er rate of reacton.


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c6 Effect of Te"perat're on ROR

"e #netc ener+y of reacting particles will ncreaparticles mo-es faster.

"us t"e number of collision among t"e reacting

increases. Fre&'ency of collson is $+$er.

"us t"e number of collision ac"ie-ed t"e acti-ation

become effecti-e collision is also increases.

"is lead to an ncrease in t"e fre&'ency of effect(e

Hence a $+$er rate of reacton.

"en t"e te"perat're of a reactant ncreases*


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)6 Effect of Catalyst on ROR

9efnton

Catalyst is a substance which alters

the rate of reaction while it remainschemically unchanged at the end ofthe reaction.


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)6 Effect of Catalyst on ROR

Propertes of Catalyst

"nergy

#eactant

"a

$roduct

"a : %cti&ation energy

'it(out catalyst

"c : %cti&ation "nergy

'it( catalyst

"c

#eaction 'it( catalyst

#eaction 'it(out catalyst

#eaction )at(

"en t"e catalyst is presence• "e catal#st allows t"e rea

t"roug" an alternat(e patlower act(aton ener+y E

• "us "ore collson ampartcles are able to a

acti-ation energ#.• "us t"e number of coll

acti-ation energ# to

collson is also ncreases.• "is lead to an ncrease in

effect(e collson.• Hence a $+$er rate of rea


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e6 Effect of Press're on ROR

"e n'"4er of partcles per 'nt (ol'"e of t"e gas oreactant also ncreases.

"us t"e number of collision among t"e reacting parti

increases. "e fre&'ency of collson is ncreases.

"us t"e number of collision ac"ie-ed t"e acti-ation e

become effecti-e collision is also increases.

"is lead to an ncrease in t"e fre&'ency of effect(e

Hence a $+$er rate of reacton.

• "en t"e press're of t"e gas of a reactant ncreases

Chapter 1 Form 5 Chemistry 2015

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