Notes factors affecting the rate of reaction

CHAPTER 1: RATE OF REACTION FACTORS AFFECTING THE RATE OF REACTION

1

TYPES OF FACTOR EXAMPLES OF REACTION EFFECT OF FACTOR ON THE RATE OF

REACTION

SIZE OF REACTANT /

TOTAL SURFACE AREA

A reaction between calcium

carbonate and hydrochloric acid

CaCO3 + 2HCl → CaCl2 + H2O + CO2

1. When the size of reactant become

smaller, the total surface area becomes

larger

2. Thus, the rate of reaction higher

ACTIVITY

Set 1 Excess calcium carbonate powder + 50 cm3 of 0.2M hydrochloric acid

Set 2 Excess calcium carbonate granulated + 50 cm3 of 0.2M hydrochloric acid

Volume of CO2 gas (cm3)

Set 1

Set 2

Time (s)

The gradient of the curve Set 1 is steeper than curve Set 2.

The rate of reaction in Set 1 is higher than rate of reaction in Set 2.

Because: The total surface area of calcium carbonate powder is larger than

calcium carbonate granulated.

The quantities of calcium carbonate and hydrochloric acid used, in mole in both

Set 1 and Set 2 are same.

Thus, the maximum volume of carbon dioxide gas collected in both Set 1 and Set

2 also the same.


2


REACTION

CONCENTRATION OF

SOLUTION (REACTANT)

A reaction between sodium

thiosulphate, Na2S2O3 solution and

sulphuric acid, H2SO4

Na2S2O3 + H2SO4 → Na2SO4 + SO2 +

H2O + S

Ionic equation:

S2O32- + 2H+ → SO2 + H2O + S

1. When concentration of Na2S2O3 solution

increases, the number of S2O22- ion per

unit volume increase.

2. Thus, rate of reaction higher.

OBSERVATION:

When the concentration of Na2S2O3 solution increases, the time taken for the ‘X’ mark

disappears from view become shorter. (yellow sulphur precipitate is formed)

Concentration of Na2S2O3

(mol dm-3)

Time

(s)

The higher the concentration, the

shorter the time taken for ‘X’ mark

disappears from view.

Thus, the rate of reaction is higher.

Concentration of Na2S2O3

(mol dm-3)

1/t

(s-1)

Concentration of Na2S2O3 is directly

proportional to rate of reaction.

The higher the concentration, the

rate of reaction is higher.


3

ACTIVITY

Set 1 Excess zinc powder + 20 cm3 of 0.4M sulphuric acid

Set 2 Excess zinc powder + 40 cm3 of 0.2M sulphuric acid

Volume of H2 gas (cm3)

Set 1

Set 2

Time (s)



Because: The concentration of sulphuric acid in Set I is higer than Set 2.

The quantities of zinc powder and sulphuric acid used, in mole in both Set 1 and

Set 2 are same.

Thus, the maximum volume of hydrogen gas collected in both Set 1 and Set 2 also

the same.


4


REACTION

TEMPERATURE A reaction between sodium

thiosulphate, Na2S2O3 solution and

sulphuric acid, H2SO4

Na2S2O3 + H2SO4 → Na2SO4 + SO2 +

H2O + S

Ionic equation:

S2O32- + 2H+ → SO2 + H2O + S

1. When temperature of a solution increase,

the kinetic energy of S2O32- ions

increases.

2. S2O32- ions move faster and have more

energy.

3. Thus, the rate of reaction higher.

OBSERVATION:

When the temperature of Na2S2O3 solution increases, the time taken for the ‘X’ mark

disappears from view become shorter. (yellow sulphur precipitate is formed)

Temperature (°C)

Time

(s)

The higher the temperature, the

shorter the time taken for ‘X’ mark

disappears from view.

Thus, the rate of reaction is higher.

Temperature (°C)

1/t

(s-1)

Temperature of Na2S2O3 is directly

proportional to rate of reaction.

The higher the temperature, the rate

of reaction is higher.


5

ACTIVITY

Set 1 1 g of CaCO3 chips + 50 cm3 of 0.5M HCl at 60.0 °C

Set 2 1 g of CaCO3 chips + 50 cm3 of 0.5M HCl at 30.0 °C

Volume of CO2 gas (cm3)

Set 1

Set 2

Time (s)



Because: The temperature of HCl in Set I is higer than Set 2.

The quantities of CaCO3 and HCl used, in mole in both Set 1 and Set 2 are same.

Thus, the maximum volume of CO2 gas collected in both Set 1 and Set 2 also the

same.


6


REACTION

CATALYST a. Decomposition of hydrogen

peroxide

In the presence of a catalyst

(manganese (IV) oxide, MnO4)

2H2O2 → 2H2O + O2

b. Reaction between zinc and

sulphuric acid

Zn + H2SO4 → ZnSO4 + H2

The rate of reaction higher when:

1. There is presence of catalyst in the

reaction

NOTE:

A catalyst – A substance which can alter the rate of reaction while its remains

chemically unchanged at the end of the reaction.

Classified into 2 types:

Positive catalyst – a catalyst that increase the rate of reaction

Negative catalyst (inhibitors) – a catalyst that lower the rate of reaction

A catalyst does not change the quantity of the products formed.

The characteristic of a catalyst:

It remains chemically unchanged at the end of the reaction.

It does not change the quantities of products formed.

The amount of catalyst remains unchanged before and after the reaction.

Most catalyst is transition element.

Only a small amount of catalyst used will increase the rate of reaction.

ACTIVITY 1

Set 1 2 g of granulated Zn + 25 cm3 of 0.1M HCl + CuSO4 solution

Set 2 2 g of granulated Zn + 25 cm3 of 0.1M HCl

Volume of H2 gas (cm3)

Set 1

Set 2

Time (s)



Because: The Set 1 is using the catalyst and Set 2 is without catalyst.

The quantities of Zn and HCl used, in mole in both Set 1 and Set 2 are same.

Thus, the maximum volume of H2 gas collected in both Set 1 and Set 2 also the

same.


7

ACTIVITY 2

Set 1 50 cm3 of 20-volume H2O2 + 0.2 g of manganese(IV) oxide, MnO4

Set 2 50 cm3 of 20-volume H2O2 + 0.8 g of manganese(IV) oxide, MnO4

Volume of O2 gas (cm3)

Set 2

Set 1

Time (s)



Because: The Set 2 is using more amount of catalyst than Set 1.

The quantities of H2O2 used, in mole in both Set 1 and Set 2 are same.

Thus, the maximum volume of O2 gas collected in both Set 1 and Set 2 also the

same.


REACTION

PRESSURE

Only reactions that involve

gaseous reactants

Reaction of hydrogen peroxide

2H2O2 → 2H2O + O2

1. When the pressure of the gas increase,

H2O2 particle per unit volume increase.

2. The reaction occurs faster.

3. Thus, the rate of reaction higher

ACTIVITY

Volume of O2 gas (cm3)

Set 1

Set 2

Time (s)



Because: The pressure in Set 1 is higher than in Set 2.


8

APPLICATION OF THE FACTORS AFFECTING THE RATE OF REACTION IN DAILY LIFE AND IN INDUSTRIAL

PROCESS

1. APPLIED IN DAILY LIFE

a. Burning of charcoal

Why food can be cooked faster when smaller pieces of

charcoal are used compared to bigger pieces of

charcoal?

ANSWER:

Smaller pieces of charcoal have bigger total

exposed surface area.

It can burn faster to produce more heat.

Thus, the food is cooked faster.

b. Storing food in a refrigerator

Why food stored in the refrigerator last longer than

the food stored in the kitchen cabinet?

ANSWER:

The temperature inside the refrigerator is lower

than kitchen cabinet.

Bacteria are not active at low temperature.

The growth of bacteria in food can be reduced.

The rate of decomposition of food is lower.

Thus, the food can be stored longer.

c. Cooking food in a pressure cooker

Why cooking of food in a pressure cooker save energy

and time (cooked faster) compared to the normal

cooker?

ANSWER:

In a pressure cooker, the high pressure raises the

boiling point of water to a temperature above 100

°C.

Thus, cooking is carried out at a temperature

higher than 100 °C in the pressure cooker.

The food can be cooked faster.

d. Cooking solid food in different sizes

Why meat cut into small pieces can be cooked faster

compare with meat in big chunks?

ANSWER:

Meat in small pieces has larger total surface than

meat in big chunks.

A total surface area exposed to heat during

cooking is increases.

More heat can be absorbed faster.

Meats in small pieces take shorter time to cook

compare to big chunks.

2. APPLIED IN INDUSTRIAL PROCESS

Name of process Haber process Contact process Ostwald process Hydrogenation

Catalyst Iron powder, Fe Vanadium(V) oxide,

V2O5 Platinum, Pt Nickel, Ni

Temperature 450 – 550 °C 450 °C 850 °C 180 °C

Pressure 200 – 300 atm 1 – 3 atm 2 – 5 atm 1 atm

Product Ammonia gas, NH3 Sulphuric acid, H2SO4 Nitric acid, HNO3 Margarine (from

palm oil)

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Notes factors affecting the rate of reaction