A reaction is fast , the time taken for the reaction is short .

A reaction is slow, the time taken for the reaction is long .

The rate of reaction depends to the speed of reaction .

If a reaction is fast, its rate of reaction is high .

If a reaction is slow, its rate of reaction is low .

The rate of reaction is inversely proportional (berkadar songsang ) with time .

Rate ά 1

time taken for reaction

Rate of reaction = change in quantity of product / reactant

time taken

For gas product , rate of reaction = volume of gas

time

From a graph , the average rate of reaction = the gradient ( kecerunan) of graph

Determine the rate of reaction

(a) Average rate of reaction

(b) Rate of reaction at a given time ( pada masa tertentu )

Example (a) :

CaCO3 + 2HCl CaCl2 + H2O + CO2

If 20 cm3 of carbon dioxide, CO2 is released in 10 seconds for the above reaction, therefore, the average rate of reaction can be calculate as :

Average rate of reaction = total volume of gas released = 20 cm3 = 2cm3 s-

total time taken 10s

Average rate of reaction = change in amount of reactant or product

time taken Example :

CaCO3 + 2HCl CaCl2 + H2 O + CO2

reactant Product

Example (b) :

The graph below shows the volume of carbon dioxide ,CO2 released against time for the reaction between calcium carbonate , CaCO3 and dilute hydrochloric acid, HCl . Determine the rate of reaction at the 20th second.

Rate of reaction at the 20th second = p

q

= ( 60 - 30 ) cm3

( 40 - 0 ) s

= 0.75 cm3 s-

10 20 30 40 50 60 70 80

10

20

30

40

50

60

Volume of gas / cm3

Time / s

p

q

P = 60 - 30

Q = 40 - 0

0

The rate of reaction decreases with time bacause :-

the concentration of a solution is decreasing as time .

Mass of reactant is decreasing as time .

The steeper (semakin curam) the gradient of the graph ,the higher the rate of reaction .

t3

Volume of gas

Time

The gradient of the graph is zero. The rate of reaction at time t3 is zero (the reaction has stopped ).

Example 1

Mg + 2HCl MgCl2 + H2

Determine the

(a)Average rate of reaction at 50 seconds.

(b)Rate of reaction at 55 seconds .

(c)Maximum number of moles of gas released .

(d)Concentration of hydrochloric acid .

(e)Mass of magnesium that reacted .

( Relative atomic mass ; Mg = 24 . Molar volume : 24 dm3 mol-1 at room condition . )

50

360

Maximum volume of gas

Time /s

Volume of gas / cm3

The graph shows the change in volume of gas with time for the reaction between excess magnesium and 25 cm3 of hydrochloric acid .

Solution

(a) Average rate of reaction in 50 seconds = 360 = 7.2 cm3 s-1

50

(b) Rate of reaction at 55 seconds = 0 cm3 s-1 (zero )

© From the graph, the maximum volume of gas released is 360 cm3 .

The maximum number of moles of volumes of gas released = volume of gas = 360

molar volume 24000

= 0.015 mol(d) Mg + 2HCl MgCl2 + H2

V = 25 cm3 ,

M = ?

1 mol of H2 gas produced by 2 mol of HCl

0.015 mol of H produced by 0.015 X 2 mol of HCl = 0.03 mol of HCl

The number of moles of HCl = MV / 1000

M = 0.03 X 1000 = 1.2 mol dm-3

25

(e) Mg + 2HCl MgCl2 + H2

Mass =?

1 mol of H2 produced by 1 mol of Mg

0.015 mol of H2 produced by 0.015 mol of Mg

The number of moles of Mg = mass / RAM

0.015 = mass

24

Mass of Mg = 0.015 X 24 = 0.36 g

2. 6.5 g of zinc powder was mixed with dilute nitric acid , HNO3 in excess. It was found that it took 50 seconds for all the gas produced to be collected . Calculate the average rate of reaction in cm3 s-1 .

( Relative atomic mass : Zn ,65 : Molar volume : 24 dm3 mol-1 at room condition )

Ans : 48 cm3 s-1

The smaller the size of particles ,the larger the total surface area , the rate of reaction will be higher .

Small total

surface area

Large total surface area

The higher the concentration of a reactant ,it have more particles per unit volume . The rate of reaction will be higher.

A shorter time is required to complete the reaction .

The higher the temperature of the reaction, the particles obtain more kinetic energy . Therefore ,the rate of reaction will be higher .

A catalyst will change the rate of reaction .

A catalyst only changes the rate of reaction but not the quantity of products.

A catalyst does not undergo any chemical change at the end of the reaction .

Pressure can affect the rate of reaction only if it involves gases.

A higher pressure can increase the rate of reaction .

The increase of pressure will compress the gas.

The particles of a gas will collide more frequently when in a compressed state (smaller volume).

To study the effect of the size of reactant on the rate of reaction.

From graph :-

The rate of reaction between the small marble chips and dilute hydrochloric acid is higher compared to the rate of reaction between the large marble chips and dilute hydrochloric acid.

The smaller the size of the reactant, the higher the rate of reaction . A smaller reactant size has a larger total exposed surface area.

The rate of reaction for both experiments decreases with time because :-

the mass of marble becomes decreases

the size of marble chips becomes decreases

the concentration of hydrochloric acid becomes decrease .

Volume of gas

Time

Marble powder

marble pieces

Maximum volume of gas in both experiments at the end of the reaction is the same because the volume , concentration and the mass of marble used in both experiments are the same.

Maximum volume of gas in both experiments at the end of the reaction is the same because the volume , concentration and the mass of marble used in both experiments are the same.

Ionic equation : S2 O32- + 2H+1 H2 O + SO2 + S

From graph (a):

It takes a longer time to form the sulphur precipitate if the concentration of sodium thiosulphate is low .

It takes a shorter time to form the sulphur precipitate when the concentration of sodium thiosulphate is high .

From graph (b),

the rate of reaction is high when the concentration of sodium thiosulphate is high .

the concentration of sodium thiosulphate solution is directly proportional to 1/time or rate of reaction .

Th

e e

ffe

ct o

f

Eff

ect

of

tem

pe

ratu

re

From a graph (a):-

A shorter time is needed for sulphur to precipitate at a higher temperature.

A longer time is needed for sulphur to precipitate at a lower temperature .

From a graph (b) :

The rate of reaction will increase when the temperature of the reactant increases .

The rate of reaction doubles each time the temperature increases by 100C .

Effect of

Hydrogen peroxide H2O2 , decomposes at a faster rate of reaction after the presence of the catalyst ,manganese (IV) oxide, MnO2 to release oxygen O2 gas. 2H2O2 2H2 O + O2

The rate of decomposition of hydrogen peroxide can be increased by increasing the amount of catalyst .

The rate of decomposition of hydrogen peroxide decreases with time because the concentration of hydrogen peroxide is decrease when the time increases .

Maximum volume of gas in both experiments at the end of the reaction is the same because the volume and concentration of hydrogen peroxide solution used in both experiments are the same.

Maximum volume of gas in both experiments at the end of the reaction is the same because the volume and concentration of hydrogen peroxide solution used in both experiments are the same.

Collision theory states that before any chemical reactions can occur, particles of the reactants have to collide with each other .

Effective collision ---- collision that produces chemical reactions by achieving the minimum energy and correct collision orientation .

Colliding particles must have equal or be more than the activation energy ( tenaga pengaktifan ) .

Activation energy is the minimum energy needed by the reactant particles to react .

H

H

I

I

I

I

H

H

Correct collision orientation Effective collision Reaction happens

IH

IH

Energy released to its surroundings causes the

total energy of the products formed to be

lower than the total energy of its reactants.

Energy released to its surroundings causes the

total energy of the products formed to be

lower than the total energy of its reactants.

Energy

Products

reactants

Activation energy

Ea

Release of heat

ENERGY

PRODUCTS

REACTANTS

Activation energy

Ea

Energy is absorbed from its surroundings causes the total energy of the products formed to be higher than the total

energy of its reactants

Energy is absorbed from its surroundings causes the total energy of the products formed to be higher than the total

energy of its reactants

Absorption of heat

(i) Collision frequency (the number of collision in one second).

The rate of reaction depends on : The rate of reaction depends on :

If the number or frequency of collisions is high, the number of collisions that occur is high .

The frequency of effective collisions also increase, therefore the rate of reaction becomes higher .

(ii) Magnitude of activation energy .

Activation energy increases , the number of collisions for a reactant particles can achieved high activation energy.

The number of effective collisions is small.

The rate of reaction will decrease .

The rate of reaction increases when the size of the particles is smaller .

The total surface area that is exposed to collision between particles are larger .

The collision frequency will increase.

Caused the effective collision frequency will increase .

The rate of reaction also increases.

Less collision between particles

More collision between particles

The rate of reaction increases if the concentration of a reactant is increase.

A higher concentration of the solution increases, the number of particles per unit volume also increases.

Can caused the frequency of collisions increase .

Thus, the frequency of effective collisions will increase.

Therefore , the rate of reaction increases .

Less collision between particles

More collision between particles

Particles

When the temperature of the reactant is increased, the rate of reaction increase too .

because the kinetic energy of particles increase.

The particles of the reactant move faster .

The number of particles which achieved activation energy also increases.

The frequency of collisions between particles also increases .

The effective collision frequency between the particles increases .

The rate of reaction will increase too .

Can increase the rate of reaction by lowering activation energy of a reaction .

Provides an alternative pathway ( lintasan alternatif ) that requires a lower activation energy .

More particles will have effective collision that has a lower activation energy .

The frequency of effective collisions increase .

The rate of reactionj will increase too.

Ea

Eb

Energy

Ea : Activation energy without catalyst

Eb : Activation energy with catalyst .

Alternative pathway

MnO2

Fe

Platinum( Pt )

V2 O5

Influences the rate reactions involving gas reactants / product.

pressure increases when the volume of the gases is reduced .

collision frequency between particles increases which caused the frequency of effective collisions increases too .

more particles have activation energy .

thus , the rate of reaction increases.

APPLICATION

• Keeping food in the refrigerator

• Burning of fuels

• Cooking food with pressure cookers

• Cooking food with small pieces will get cooked faster .

• Use of catalyst in industry .

vanadium(v) oksida - catalystvanadium(v) oksida - catalystThe raw materials --- sulphur and air Sulphur is burnt in air , sulfur dioksida terhasilS + 0 2 S02

Sulfur is oxidised to sulfur dioxide

vanadium(v) oksida - catalystvanadium(v) oksida - catalystThe raw materials --- sulphur and air Sulphur is burnt in air , sulfur dioksida terhasilS + 0 2 S02

Sulfur is oxidised to sulfur dioxide

sulphur dioxide is mixed with dry oxygen is passed over vanadium (V) oxide, (catalyst) at a temperature of 450 – 500 0C and a pressure of 1 Atmosphere (atm)

sulphur dioxide is mixed with dry oxygen is passed over vanadium (V) oxide, (catalyst) at a temperature of 450 – 500 0C and a pressure of 1 Atmosphere (atm)

Sulphur trioxide gas is dissolved in concentrated

sulphuric acid to produce oleum

SO3 + H2SO4 H2 S2 O7 (oleum)

Sulphur trioxide gas is dissolved in concentrated

sulphuric acid to produce oleum

SO3 + H2SO4 H2 S2 O7 (oleum)

Oleum is diluted with an equal volume of water

To produced concentrated sulphuric acid . H2 S2O7 + H2O 2H2SO4

Oleum is diluted with an equal volume of water

To produced concentrated sulphuric acid . H2 S2O7 + H2O 2H2SO4

Ammonia is oxidised to nitrogen monoxide by oxygen. The presence of platinum ( catalyst ).

Temperature 8500 – 9000 C & pressure 5 atm.

4NH3 + 5O2 4NO + 6H20

Nitrogen dioxide is dissolved in water to produce nitric acid . 4NO2 + O2 + 2H2 O 4HNO3

Nitrogen monoxide is oxidised to nitrogen dioxide

2NO + O2 2NO2

Gas hidrogen dan nitrogen bertindak balas pada suhu 4500 - 5500 C , tekanan 200 – 500 atm dan dibantu oleh mangkin ( serbuk ferum ) Bahan penggalak ialah molibdenum

N2 + 3H2 2NH3

PREPARED BY

PN ZAINAB BT AYUB