1. Factors Affecting Rate of Reaction - Explanation by Collision Theory
Size of Reactants
1. When the size of the solid substance that reacts is smaller, its total surface areaexposed
becomes larger.
2. This causes the collisions frequency between the reactants increases.
3. As a result, the frequency of effective collisions also increases and hence increases the rate of
reaction.
Concentration
1. Solution with higher concentration has more particles per unit volume in the solution.
2. As a result, the collisions frequency between the reactants increases.
3. Consequently, the frequency of effective collisions also increases and hence the rate of reaction
increases.
Temperature
1. When the temperature of a reaction increases, the particles of the reacting substances move
faster.
2. This causes the collisions frequency between the reactants increases.
3. As a result, the frequency of effective collisions also increases and hence increases the rate of
reaction.
Presence of Catalyst
1. When a catalyst is used in a reaction, the catalyst prepares an alternative path with lower
activation energy for the reaction.
2. As a result, the frequency of effective collisions increases and hence increases the rate of
reaction.
Pressure of Gas
1. For a reaction that involves a gas, when pressure increases, the particles of gas are compressed
to fill the spaces which are small. This makes the number of particles of gas per unit of volume
to increase.
2. This causes the collisions frequency between the reactants increases.
3. As a result, the frequency of effective collisions also increases and hence increases the rate of
reaction.
Factors Affecting –Size of reactants
1. For reaction involves solid reactant, when the solid reactants is broken up into smaller pieces,
the total surface area of the reactant become bigger.
2. The bigger the total surface area of the reactant, the higher the rate of reaction.

2. a.
b.
The smaller the size of the particle, the bigger the total surface area.
The bigger the total surface area, the higher the rate of reaction.
Experiment
The reaction between Hydrochloric acid, HCl and calcium carbonate, CaCO3.
CaCO3+2HCl→CaCl2+CO2+H2O
Experiment 1
25 cm3 of 0.5 moldm–3 hydrochloric acid + calcium carbonate chips. The carbon dioxide gas released is
collected in a burrete. The volume of the gas released is recorded in every 30s. The result is plotted in a
graph.
Experiment 2
25 cm3 of 0.5 moldm–3 hydrochloric acid + calcium carbonate powder. As in experiment 1, the carbon
dioxide gas released is collected in a burrete and the volume of the gas released is recorded in every
30s. The result is plotted in the same graph in experiment 1.

3. Conclusion
/s
1. The gradient of the curve for experiment 2 is greater than the curve for experiment 1. This
indicate that the rate of reaction in experiment 2 is higher than experiment 1.
2. We can conclude that, the smaller the particle size of the reactant, the bigger the total surface
area, and the bigger the total surface area, the higher the rate of the reaction will be.
Factors Affecting - Concentration of Reactants
The higher the concentration of the solution, the higher the rate of reaction.
Experiment
By measuring the time taken for the formation of sulphur precipitate (yellow solid) when sulphuric acid,
H2SO4 reacts with sodium thiosulphate(VI), Na2S2O3 of different concentration , we can investigate the
effect of concentration of the reactant on the rate of reaction.
Procedure:
1. 50 cm3 of 0.2 mol dm-3 sodium thiosulphate solution + 10 cm3 of 0.5 mol dm-3sulphuric acid.
2.
X’ sign placed under the conical flask to disappear from view is recorded.

4. 3. The experiment is repeated by using sodium thiosulphate solution with concentration 0.4 mol
dm-3, 0.6 mol dm-3, 0.8 mol dm-3 and 1.0 mol dm-3.
Conclusion 1:
1. The graph for concentration of sodium thiosulphate (VI), Na2S2O3 against time taken for the
sulphur precipitate to formed is plotted.
2.
X’ to disappear.
Conclusion 2:
1. The graph for concentration of sodium thiosulphate (VI), Na2S203 against 1/time taken is
plotted.
2. As the concentration of sodium thiosulphate increases, the value of 1/time increases. We
should note that 1/time = rate of reaction.
3. The higher the concentration of sodium thiosulphate solution, the higher the rate of reaction .

5. Factors Affecting - Temperature of the Reactant
The higher the temperature of the solution, the higher the rate of reaction.
Experiment
By measuring the time taken for the formation of sulphur precipitate (yellow solid) when sulphuric acid,
H2SO4 reacts with sodium thiosulphate(VI), Na2S2O3 of different temperature, we can investigate the
effect of temperature of the reactant on the rate of reaction.
Procedure:
1. 50 cm3 of 0.2 mol dm-3 sodium thiosulphate solution at 30ºC + 10 cm3 of 0.5 mol dm-3 sulphuric
acid.
2.
X’ sign placed under the conical flask to disappear from view is recorded.
3. The experiment is repeated by using sodium thiosulphate solution with temperature 35ºC, 40ºC,
45°C and 50°C.
Conclusion 1:

6. 1. The graph for temperature of sodium thiosulphate (VI), Na2S2O3 against time taken for the
sulphur precipitate to formed is plotted.
2. As the temperature of sodium
X’ to disappear.
Conclusion 2:
1. The graph for temperature of sodium thiosulphate (VI), Na2S203 against 1/time taken is plotted.
2. As the temperature of sodium thiosulphate increases, the value of 1/time increases. We should
note that 1/time = rate of reaction.
3. The higher the temperature of sodium thiosulphate solution, the higher the rate of reaction .
Factors Affecting - Presence of Catalyst
1. A catalyst is a substance which can change the rate of reaction.
Experiment 1
Set 1: Zinc + Hydrochloric Acid
Set 2: Zinc + Hydrochloric Acid + Copper Sulphate (Catalyst)
Chemical Reaction:
Zn + 2HCl → ZnCl2 + H2

7. Result:
/s
Copper(II) sulphate acts as a catalyst to increase the rate of reaction between zinc and hydrochloric acid
Conclusion
The presence of catalyst increases the rate of reaction.
Experiment 2
Set 1: Decomposition of Hydrogen Peroxide
Set 2: Decomposition of Hydrogen Peroxide + Manganese(IV) Oxide(Catalyst)
Chemical Reaction:
2H2O2 → 2H2O + O2
Result:
/s
Manganese(IV) oxide acts as a catalyst to increase the rate of reaction between zinc and hydrochloric
acid

8. Conclusion:
The presence of catalyst increases the rate of reaction
Factors Affecting - Pressure of Gas
1. For reactions involve gas, the rate of reaction is affected by the pressure of the gas.
2. Pressure DOES NOT affect the rate of reaction where the reactants are in the form of solids or
liquids.
3. The higher the pressure of the gas, the higher the rate of reaction
The higher the pressure of the gas, the higher the rate of reaction