1.2 Factors Affecting the Rate of Reaction

The factors
■ Factors that affect the rate of a reaction, including

	►	physical state (size and surface area) of the materials response
	►	the concentration of the reaction materials
	►	temperature
	►	pressure
	►	the presence of a catalyst

■ This video shows on the factors that affect the rate of reaction.

■ This video contains information on the factors affecting the rate of reaction.

Size of the reactants
■ Size of the reactants

	►	When a solid reacts with a liquid or gas, the size of the solid reactant will affect the rate of reaction.
	►	The smaller the reactant size, the larger the total exposed surface area.
	►	Thus, the rate of reaction will be higher.

■ Graph of rates of reaction

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The following graph shows the effect of reactant surface area on the rate of reaction for the reaction between calcium carbonate and hydrochloric acid.

■ This video contains information on the graphs of rates of reaction.

Laboratory Activity 1.2.1: The Effect of Surface Area on the Rate of Reaction

The Effect of Concentration
■ Effect of the concentration

	►	The concentration of reactant affect the rate of reaction in liquid form.
	►	The higher the concentration, the more particles per unit volume.
	►	Thus, the rate of reaction will be higher.

✍ Worked-example 1.2(a) An experiment is carried out to study the rate of reaction between zinc powder and hydrochloric acid at different concentration. The following table shows five experiments that have been carried out to study the effect of concentration on the rate of reaction. Experiment I: 50cm3 of 1mol dm-3 HCl in excess of zinc powder. Experiment II: 100cm3 of 2mol dm-3 HCl in excess of zinc powder. Experiment III: 150cm3 of 0.5mol dm-3 HCl in excess of zinc powder. Experiment IV: 25cm3 of 1.5mol dm-3 HCl in excess of zinc powder. Experiment V: 100cm3 of 0.5mol dm-3 HCl in excess of zinc powder. Sketch the graph that show the volume of carbon dioxide gas released against time by comparing conditions in each experiment versus Experiment I. Solution: ► Experiment I versus Experiment II ► Experiment I versus Experiment III ► Experiment I versus Experiment IV ► Experiment I versus Experiment V

Laboratory Activity 1.2.2: The Effect of Concentration of the Reactant on the Rate of Reaction

The Effects of temperature
■ Effect of the temperature

	►	When the temperature of the reaction increases, more particles obtain higher kinetic energy.
	►	Thus, the rate of reaction will be higher.

■ Graph of rates of reaction

	►	The following graph show the effect of temperature on the rate of reaction for the reaction between calcium carbonate and hydrochloric acid.

Laboratory Activity 1.2.3: The Effect of Temperature of the Reactant on the Rate of Reaction

Effects of catalyst
■ Catalyst

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A substance that can change the rate of chemical reactions but does not affect the amount of product formed.

■ Characteristic of catalysts

	►	Does not affect the amount of product obtained.
	►	Only affects the rate of reaction.(A positive catalyst will increase the rate of reaction while a negative catalyst will decrease the rate of reaction)
	►	Specific action on a particular reaction.
	►	Only a small amount of catalyst is needed.
	►	Chemically unchanged at the end of the reaction.(It may change physically)

■ Graph of rates of reaction

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The following graph shows the effect of catalyst on the rate of reaction for the decomposition of hydrogen peroxide catalyzed by powdered manganese (IV) oxide. ○ Chemical equation: 2H2O2(aq) → 2H2O(aq) + O2(g) ○ Observation: Hydrogen peroxide decomposes to release oxygen gas. ○ Suitable method to measure rate of reaction: Volume of oxygen gas released.

Laboratory Activity 1.2.4: The Effect of Catalyst of the Reactant on the Rate of Reaction

Effects of pressure on the rate of reaction
■ Effect of the pressure

	►	Pressure will affect the rate of reaction of gaseous reactant.
	►	When the pressure of gas increases, the particles of gas will collide more frequently.
	►	Thus, the rate of reaction will be higher.

■ Example: Production of ammonia through Haber process in industry.

	►	Chemical equation: N2(g) + 3H2(g) ⇌ 2HN3(g)
	►	The Haber process is carried out at pressure of 200 – 500 atmosphere.

Application of factors affecting the rate of reaction in daily life
■ Effect of the pressure

	►		Combustion of charcoal
	►		Storing food in refrigerator
	►		Cooking food in pressure cooker

Application of factors affecting the rate of reaction in industry
■ The production of ammonia by the Haber process

	►	N2(g) + 3H2(g) ⇌ 2NH3(g)
	►	Nitrogen and hydrogen are mixed in the ratio of 1 : 3 volumes and passed over iron fillings(catalyst) mixed with aluminium oxide at 450-550℃ and optimum pressure 200 atmospheres.

■ Contact Process for the manufacture of sulphuric acid

	►	Step I: Production of sulphur dioxide gas, SO2 S(s) + O2 → SO2(g)
	►	Step II: Conversion of sulphur sulphide to sulphur trioxide, SO3 2SO2(g) + O2(g) ⇌ 2SO3(g) The gas mixture is passed over vanadium(V) oxide, V2O5(catalyst) at temperature 450-500℃ and under the pressure of 1 atmosphere.
	►	Step III: Production of sulphuric acid, H2SO4 SO3(g) + H2SO4(l) → H2S2O7(l)

■ The production of nitric acid by the Ostwald process

	►	Step I: 4NH3(g) + 5O2(g) ⇌ 4NO(g) + 6H2O(l) The gas mixture is passed over platinum, Pt (catalyst) at temperature 850℃.
	►	Step II: 2NO + 2O2(g) → 2NO2(g)
	►	Step III: NO(g) + O2(g) + 2H2O2(l) → 4HNO3

■ Cracking of Petroleum hydrocarbons

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The alkane(large hydrocarbons molecules) is brought into contact with aluminosilicate(catalyst) at a temperature of about 500℃ and pressures of 1 atmosphere.

■ Manufacture of margarine

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The transition metal nickel is used in the hydrogenation of vegetable oils to make margarine at a temperature of about 180℃ and pressures of 1 atmosphere.

■ This video contains information on the application of factors affecting the rate of reaction.