10 rate of reaction

RATE OF REACTION

1. Concept Map

2. Rate of reaction

(a) Rate of reaction is the s………………at which reactants react to form products in a

chemical reaction.

(b) Classify the following reaction as fast or slow reaction

No. Example Fast or Slow Reaction1 Corrosion of iron nail2 Striking a match3 Photosynthesis4 Neutralization5 Acid with reactive metal6 Ripening of manggo

(c) For a fast chemical reaction

Time taken for the reaction to complete is s………………..

The reactants are q……………… converted to the products

The rate of reaction is h…………………

CHEMISTRY MODULE 2009© HAK MILIK JPN PAHANG

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Rate of reaction

Observable changes in chemical reaction

Average rate of reaction Rate of reaction at a given time

Factors affecting rate of reaction

Collision Theory to explain factors affecting rate of reaction

(d) For a slow chemical reaction

Time taken for the reaction to complete is l………………..

The reactants are s……………… converted to the products

The rate of reaction is l…………………

(e) The rate of reaction can be determined by measuring the time taken for an

observable chemical change to occur.

Rate of reaction = Observable chemical change Time taken

(f) The observable chemical changes in a chemical reaction are

(i) …………………………………………………………………………….

(ii) ……………………………………………………………………………

(iii) ………………………………………………………………………….

(iv) …………………………………………………………………………

(v) …………………………………………………………………………..

(g) Definition:

Rate of reaction is the change of amount of reactant / product per unit time.

Example:

(i) If 50.0 cm3 of hydrogen gas is collected in 20 seconds during a chemical

reaction between magnesium and dilute hydrochloric acid . What is the rate of

reaction?

Rate of reaction = = cm3 s-1


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Rate of reaction α ………………..

(ii) If time taken for 5.0 gram of magnesium ribbon reacts completely with dilute hydrochloric acid is 25s, what is the rate of reaction?

Rate of reaction = = g s -1.

3. Suitable observable changes to determine the rate of reaction from graph.

For the reaction bellow

ZnCO3(s) + 2HCl(aq) → ZnCl2(aq) + CO2(g) + H2O(l)

Sketch the graph for:


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Concentration of HCl / mol dm-3

, s-1

Concentration of HCl / moldm-3

Mass of ZnCO3 / g

Time/s Time/s

Concentration of ZnCl2 / mol dm-3

Volume of CO2 gas / cm3

Time/s Time/s

(d) In a chemical reaction involving release of a gas, it is easier to determine the rate of reaction by measuring the v……………………of gas at a certain time interval.

(e) Rate of reaction can be measured as average rate of reaction or the rate of reaction

at a particular given time.

(f) Average rate of reaction is the a………………………value of the rate of reaction

within a specified period of t………………….

(g) Rate of reaction at a given time is the a……………… rate of reaction at that instant

Example: Graph of the total volume of gas liberated against time for a reaction

where gas is given off

Activity:

Table bellow shows the burette reading of hydrogen gas collected at different time

intervals when magnesium ribbon react with hydrochloric acid

Time/s 0 30 60 90 120 150 180 210 240 270 300Burette reading/cm3 50.00 36.00 25.00 17.00 11.00 8.00 6.00 5.00 4.00 4.00 4.00

Volume of gas collected/cm3


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Rate of reaction at time t1 =EFoflength

DFoflength cm3s-1

Gradient of the tangent at any point on the curve

=timeinchange

gastheofvolumeinchange

To determine the rate of reaction at a given

time t1 s

- Draw a tangent (line DE) at the point M on

the graph.

- Draw a right-angle triangle DEF

- Measure the length of DF and EF.

- Calculate the gradient of the tangent DE

Time/s

Volume of gas/cm3

EF

D

t1

M

(a) Calculate the volume of gas collected

(b) Plot a graph of volume of hydrogen gas collected against time.


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(c) Based on the graph plotted, determine

(i) the average rate of reaction in the first 2 minutes

(ii) the average rate of reaction in the second minute

(iii) the overall average rate of reaction

(iv) the rate of reaction at 1 minute

(v) the rate of reaction at 3 minutes


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(d) Compare the rate of reaction obtained in (iv) and (v). Explain your answer.

(e) Write a balance chemical equation of the reaction between magnesium and hydrochloric acid.

4. Factors affecting rate of reaction

I. Effect of total surface area of reactant on the rate of reaction.

(a) For a fixed mass of solid reactant, the smaller the size of the reactant the higher the rate of reaction

Smaller size of a solid reactant

Larger t…………………… exposed surface area

Rate of reaction is h………………………….

Examples

(i) Cube sugar dissolves slower than that of fine sugar of the same mass in

same amount of water and temperature

(ii) Meat cut into small pieces cook faster than meat cut into big lump of the

same mass.

(iii) Powdered zinc reacts faster than granulated zinc of the same mass with

hydrochloric acid of the same volume and concentration.

(b) Experiment to investigate the effect of total surface area of calcium carbonate on the rate of reaction

Problem statement:


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Hypothesis:

Variables:(i) manipulated variable:

(ii) responding variable:

(iii) fixed variable:

Materials:

Apparatus:

Procedure:(Diagram)

Results:

(i) Experiment I using large marble chips:

Time/ minute 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5Burette reading/cm3 49.50 45.20 42.0 39.00 36.50 34.00 31.80 29.50 27.80 26.20 24.50 23.50



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(ii) Experiment II using crushed marble chips:

Time/ minute 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5Burette reading/cm3 49.00 39.00 33.00 28.50 25.00 21.50 19.00 16.70 14.70 13.00 11.50 10.00


1. Plot the graph of total volume of gas collected against time taken for the reaction for experiment I and II on the same axes.

2. Based on the graph, calculate (a) the overall rate of rate of reaction for the first 5 minutes of the reaction between hydrochloric acid and

(i) large marble chips:

(ii) crushed marble chips

(b) The rate of reaction at 2.5 minute for(i) large marble chips:

(ii) crushed marble chips:

3. Based on your answers in 2(a) and 2(b), how does the rate of reaction differ?

4. What is the factor that causes the difference in rate of reaction?

5. Write a balanced chemical equation for the reaction between calcium carbonate and hydrochloric acid.

6. Explain why does the rate of reaction decreases with increase of time.


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7. If both reactions are allowed to react until completion, is the total volume of gas collected the same? Explain your answer.

8. If the marble chips used in the experiment is in excess, what is the maximum total volume of gas collected? [ 1 mole of gas at room temperature occupies a volume of 24dm3]

Conclusion:

II. The effect of concentration of reactant on the rate of reaction.

(a) When concentration of reactant increases, the rate of reaction increases.

Give one example for the above statement.

(b) Experiment to investigate the effect of concentration of sodium thiosulphate with hydrochloric acid on the rate of reaction

Problem statement:

Hypothesis:




Procedure:(Diagram)


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Results:

Experiment 1 2 3 4 5

Volume of 0.2moldm-3 sodium thiosulphate solution, V1 cm3 45 40 35 30 25

Volume of distilled water added/cm3 0.0 5.0 10.0 15.0 20.0

Volume of 1.0mol hydrochloric acid added/cm3 5.0 5.0 5.0 5.0 5.0

Total volume of reactant /cm3 50.0 50.0 50.0 50.0 50.0

Concentration of sodium thiosulphate solution used/moldm-3

Time taken/s 16 20 27 41 83


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1/time , s-1

1. Plot the graph of concentration of sodium thiosulphate solution used against time taken for the reaction.

2. Plot the graph of concentration of thiosuphate solution used against 1/time.

3. What does the value of 1/time represents?

4. Based on your graph, state the relationship between (i) the concentration of sodium thiosulphate and the time taken for the reaction.

(ii) the rate of reaction and the concentration of sodium thiosulphate solution.

5. What is colour of the precipitate formed and name the precipitate.

6. What is the time taken for the mark ‘X” to disappear if the concentration of sodium thiosulphate solution used is 0.10 mol dm-3?

7. Write a balanced chemical equation for the reaction in this experiment.

8. Write an ionic equation for the reaction in this experiment.

9. If dilute sulphuric acid of the same concentration is used to replace hydrochloric acid in this experiment, predict the rate of reaction and explain your answer.


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Conclusion:

III. The effect of temperature on rate of reaction.

(a) Increase in temperature of reaction, increases the rate of reaction.

Give two examples for the above statement. (i)

(ii)

(b) Experiment to investigate the effect of temperate on the rate of reaction between thiosulphate solution and dilute hydrochloric acid.

Problem statement:

Hypothesis:

Variables:(i) manipulate variable:



Procedure:(diagram)


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Results:

Experiment 1 2 3 4 5

Temperature/oC 30 35 40 45 50

Time taken/s 55 48 42 37 33

1/time, s-1

1. Plot the graph of (i) temperature against time and (ii) temperature against 1/time.

2. Based on your graph, what is the relationship between rate of reaction with temperature.

3. Write a balance chemical equation for the reaction of this experiment.

4. why is the volume of sodium thiosulphate solution and hydrochloric acid fixed for each experiment?

5. What is the time taken for the mark ‘X’ to disappear when the temperature is 60oC?

Conclusion:

IV Effect of catalyst on the rate of reaction.

(a) Catalyst is a substance which a…… ……….. the rate of a chemical reaction while

it remains c……………………. unchanged at the end of the reaction

(b) Special characteristic of catalyst

Catalyst alters the r………………… of a chemical reaction


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The a………………… of products formed remain unchanged with or without the

catalyst

Only a small amount of catalyst is needed to achieve a b…………change in the

rate of reaction

Increasing the amount of catalyst used generally will i………………….the rate of

reaction

Catalyst may undergo p…………………….. changes

Catalyst remains c……………………… unchanged during the reaction

The m……………..and chemical composition of the catalyst remain the same

before and after the reaction

Most catalyst are t……………………… elements or compounds of transition

elements such as iron, nickel and copper(II) sulphate, CuSO4

Catalyst is s………………………….. in its actio

Example: When copper(II) sulphate solution is added into a reaction between zinc and

sulphuric acid, the rate of reaction increases but the final quantity of hydrogen

produced is the same the reaction of zinc with hydrochloric acid without copper(II)

sulphate solution.

(c) Experiment to investigate the effect of catalyst on the rate of reaction for decomposition of hydrogen peroxide solution.

Problem statement:

Hypothesis:


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Time/s

Volume of hydrogen released/cm3

Without catalyst

With catalyst




Apparatus:

Materials:

Procedure:

Observation:

Test tube Observation

A


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B

Discussion:

1. What is the effect of manganese(IV) oxide on the decomposition of hydrogen peroxide solution?

2. What is the function of manganese(IV) oxide in this experiment?

3. Write a balanced chemical equation for the reaction in this experiment.

4. Will the mass of manganese(IV) oxide change at the end of the reaction in test tube B?

Conclusion:

(d) Experiment to investigate the effect of the amount of catalyst on the rate of reaction for decomposition of hydrogen peroxide solution.

Problem statement:

Hypothesis:




Apparatus:


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Materials:

Procedure:

Results:(i) Experiment 1, using 0.2g of manganese(IV) oxide

Time/s0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

Burette reading/cm3 49.70 48.70 47.10 45.70 44.20 43.20 42.00 41.10 40.20 39.50 39.00 38.40 38.00

Volume of gas cm3

(ii) Experiment II, using 0.6g of manganese(IV) oxide

Time/s0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

Burette reading/cm3 49.00 43.60 40.50 38.00 36.00 34.50 33.00 31.70 30.50 29.70 29.00 28.20 28.00


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Volume of gas cm3

1. Plot the graph of total volume of gas against time for experiment I and experiment II on the same axes.

2. Based on your graph, calculate the rate of reaction at 120 seconds for each of the reaction .

(i) Experiment I:

(ii) Experiment II:

3. How did the rates of reaction in experiment I and II differ?

4. Which experiment shows the higher rate of decomposition of hydrogen peroxide?

5. If both experiments are allowed to proceed until completion, is the total volume of gas collected in both experiments the same? Explain your answer.

Conclusion:

(e) Application of catalyst in industry.

Most catalysts are transition elements or compounds of transition elements. Catalyst is specific in its action and only a small amount is required in a chemical reaction.

Industrial process

Product produced

Equation Catalyst

Haber Process

Contact Process

Ostwald Process

Hydrogenation of


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vegetable oilCracking of petroleum

Activity:

1. Equation below shows the decomposition of sodium chlorate solution using

manganese(IV) oxide as a catalyst

2NaOCl(aq) → 2NaCl + O2(g)

For the following experiments, sketch graph

(i) volume of gas against time

Explain your answer

(ii) volume of gas against time

Experiment 1 5 g Magnesium + 50 cm3 of 0.5 moldm-3 hydrochloric acid at room temperatureExperiment 2 5 g Magnesium + 50 cm3 of 0.5 moldm-3 hydrochloric acid at 50OC


Experiment 1 100 cm3 of 0.5 moldm-3 NaOCl + MnO2

Experiment 2 50 cm3 of 1.0 moldm-3 NaOCl + MnO2

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Volume of oxygen/cm3

Time/s

Volume of oxygen/cm3

Time/s

Explain your answer

2. For the following experiment, sketch the graph volume of hydrogen against time

Experiment 14 g of excess zinc powder + 100 cm3 of sulphuric acid 0.5 mol dm-3 + 5cm3 copper(II) sulphate solution at room temperature

Experiment 24 g of excess zinc powder + 100 cm3 of sulphuric acid 0.5 mol dm-3 room temperature

Experiment 34 g of excess zinc powder + 50 cm3 of sulphuric acid 0.5 mol dm-3 at room temperature

Explain your answer

8. Collision Theory

(a) For a chemical reaction to occur, the particles of the reactants must collide with each other. However, not all collisions result in a chemical reaction to form products.

(b) According to collision theory, only those collisions which

with the c…………………… orientation and .

achieved a m…………………. amount of energy called activation energy , Ea

will result in chemical reaction

(c) Collisions of particles of reactants that result in chemical reaction is known as

……………………… collision

(d) Activation energy , Ea, is defined as the minimum amount of energy of collision that is required for particles of reactant to react or to produce e…………………. collision.


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Volume of hydrogen/cm3

Time/s

(i) Exothermic reaction (ii) Endothermic reaction

(e) Using Collision Theory to explain the factors affecting the rate of reaction.

1. The effect of increase in total surface area of reactant.

Using solid reactant that is smaller in size. When size of solid reactant is smaller, the total surface area increases The frequency of collision of particles of reactant increases The frequency of effective collision increases The rate of reaction increases.

2. The effect of increase in concentration of reactant.

Increasing the concentration of reactant will increase the number of particles of reactant per unit volume.

The frequency of collision of particles of reactant increases. The frequency of effective collision increases. The rate of reaction increases.

3. The effect of increase in temperature of reaction

o By increasing the temperature of the reactanto Increased in temperature, increases the kinetic energy of the reactant

particles.o The frequency of colliding particles possesses energy higher than the

activation energy increases.o The frequency of effective collision increaseso The rate of reaction increases.

4. The effect of catalyst on the rate of reaction.

Addition of a positive catalyst to a chemical reaction provides an alternative path of reaction that requires a lower activation energy.


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Energy

Reactant

Product

Ea

Energy

Reactant

ProductEa

The frequency of effective collision increases The rate of reaction increases. Energy profile diagrams to show the effect of catalyst on rate of reaction.

Exothermic Reaction Endothermic Reaction

Ea – Activation energy without energyEa’ – Activation energy with energy

V. The effect of pressure on rate of reaction.

(i) The effect of pressure only affects the rate of chemical reaction when the reactants Are in the gaseous state.

Eg: N2(g) + 3H2(g) 2NH3(g)

(ii) Increased in pressure by increasing the concentration of gas or by reducing the volume of the vessel,

o the number of particles per unit volume increases. o The frequency of collision among the reactant particles increaseso The frequency of effective collision increaseso Hence the rate of reaction increases.

Activity:

1. Complete the following table:

ExperimentFactor affect the rate of reaction

Sketch of graph Explain using collision theory


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Energy

Reactant

Product

Ea

Ea’

Energy

Reactant

Product

EaEa’

Two set of experiment is carry out between marble chip and hydrochloric acid:Exp I: Excess of zinc powder and 50 cm3 of 0.5 moldm-3 hydrochloric acidExp II: Excess of zinc granule and 50 cm3 of 0.5 moldm-3 hydrochloric acid

The rate of reaction in exp I is ……………… than exp II

The gradient of the curve for exp I is ……………. than exp II

Zinc powder has …………. total surface area

Frequency of collision of zinc and …………………. increases

Frequency of ……………… collision increases

Reinforce exercise;

1. Which of the following can be used to determine the rate of the reaction?

I Release of gas per unit time.II Change of colour intensity per unit time.III Formation of precipitate per unit time.IV Increase in the mass of reactant per unit time.

A. I and IIB. III and IVC. I, II and IIID. II, III and IV

2. An equation of a reaction is as follows

In the reaction represented by the equation above, it was found that the change of colour from green to brown was faster when the reactant mixture was heated.This was due to the…

I. decrease in the activation energy.II. increase in the frequency of effective collision .III. increase in the kinetic energy of ferrum(II) ions and chlorine molecules. IV. increase in the frequency of collision between ferrum(II) ions and chlorine

molecules.

A. I and II onlyB. II and III onlyC. I, III and IV onlyD. II, III and IV only

3. Table 4 shows the total volume of gas collected at regular intervals in a reaction.

Time / s 0 30 60 90 120 150 180 210Volume of gas/ cm3 0 2.0 3.7 5.2 6.4 7.3 8.6 8.6


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2Fe2+ + Cl2 2Fe3+ + 2ClGreen Brown

Volume of gas / cm3

Time, s

What is the average rate of reaction in the second minute ?

A. 0.040 cm3s-1

B. 0.045 cm3s-1

C. 0.053 cm3s-1

D. 0.062 cm3s-1

4. The equation below represents the decomposition of hydrogen peroxide solution.

Which of the following are produced when 1 mole of hydrogen peroxide is decomposed completely ?[1 mole of gas occupies 24 dm3 at room condition;Avogadro’s constant : 6 X 1023 mol-1]

I 2 moles of waterII 12 dm3 of oxygen gasIII 3 X 1023 of oxygen molecules IV 1.2 X 1024 of water molecules

A I and III onlyB I and IV onlyC II and III onlyD II and IV only

5 An experiment is carried out to study the rate of reaction between marble and hydrochloric acid to produce carbon dioxide gas.

Experiment SubstancesI Excess marble and 50.0 cm3 of 2 mol dm-3 hydrochloric acidII Excess marble and 100.0cm3 of 1 mol dm-3 hydrochloric acid

A C

B D


2H2O2(aq) 2H2O(l) + O2(g)

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Volume of CO2/cm3

Volume of CO2/cm3

Volume of CO2/cm3

Time/s Time/s

I

III

II

6 The reaction between hydrochloric acid and zinc produces hydrogen gas. The reaction is complete in 50 seconds and the maximum volume of gas produced is 25 cm3.What is the average rate of the reaction?

A. 0.5 cm3 s-1 C. 2.0 cm3 s-1

B. 1.0 cm3 s-1 D. 4.0 cm3 s-1

7 The diagram shows the energy profile of a reaction.Ea is the activation energy for this reaction.

What will change the activation energy from Ea to Ea’?A. Temperature C. ConcentrationB. Catalyst D. Total surface area

8 Which of the following explains the meaning of effective collision?

A. The collision where its energy is less than the activation energy.B. The collision that has a low energyC. The collision which takes place before a reactionD. The collision that causes a reaction

9 The diagram shows the set up of the apparatus for an experiment to determine the rate of reaction between sodium thiosulphate and sulphuric acid.


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Volume of CO2/cm3Time/s Time/s

I III II

Energy

Reactant

Products

Reaction path

Ea

Ea’

Which of the following combination of conditions take the shortest time for the mark ‘X’ to diappear from sight?

Sulphuric acid Sodium thiosulphate Temperature/oCVolume/cm3 Concentration/

mol dm-3Volume/cm3 Concentration/

mol dm-3

A 10 1.0 50 0.5 30B 10 1.0 50 0.5 40C 10 0.5 50 0.5 30D 20 0.5 40 0.5 40

10 In an experiment, the decomposition of 25cm3 of 0.1 mol dm-3 hydrogen peroxide solution produces oxygen gas.

If the experiment is repeated using another solution, which solution will produce curve Q?

A. 25 cm3 of 0.15 mol dm-3 hydrogen peroxideB. 20 cm3 of 0.15 mol dm-3 hydrogen peroxideC. 15 cm3 of 0.15 mol dm-3 hydrogen peroxideD. 10 cm3 of 0.25 mol dm-3 hydrogen peroxide

11 The following statements are related to the collision theory of a reaction.

I. The total surface area of the reactant particles increases.II. The kinetic energy of the reactant particles increases.III. The frequency of the collision between the reactant particles increases.IV. The number of the reactant particles per unit volume increases.

Which of the following combinations is true about the effect of the rise in temperature on the reactant particles?

A I and II only C III and IV onlyB II and III only D I and IV only


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Volume of oxygen gas/cm3

Time/s

P

Q

12 If you want to cook 100 potatoes within a short time, which is the most suitable method?

A Boil the potatoes in a panB Boil the potatoes in a pressure cookerC Steam the potatoes in a steamerD Fry the potatoes in a wok

13 Which of the following reactants produces the highest rate of reaction with zinc powder?

A 25 cm3 of sulphuric acid 0.1 mol dm-3.B 25 cm3 of ethanoic acid 0.1 mol dm-3.C 25 cm3 of nitric acid 0.1 mol dm-3.D 25 cm3 of hydrochloric acid 0.1 mol dm-3.

14 Which of the following mixture of limestone and 50 cm3 hydrochloric acid will give the highest initial rate of gas produced ?ABCD

5 g limestone powder with 0.2 mol dm-3 hydrochloric acid5 g limestone granules with 0.2 mol dm-3 hydrochloric acid10 g limestone powder with 0.1 mol dm-3 hydrochloric acid10 g limestone granules with 0.2 mol dm-3 hydrochloric acid

15 5C2O42- (aq) + 16 H+ (aq) + 2 MnO4

- (aq) → 10 CO2(g) + 8H2O (l) + 2Mn2+ (aq) Ethanadioic ion manganate (VII) ion The above equation represents the reaction between ethanadioic acid with acidic potassium manganate (VII) . If excess of acidic potassium manganate (VII) was used, the rate of reaction can be determined by theABCD

time manganese ion producedtime to decolourised the potassium manganate (VII) solutionmass of manganese salt produced at a given timetime taken to collect a certain volume of carbon dioxide

16 In a catalytic reaction, a catalyst will increase the rate of reaction because a catalyst willABCD

decrease the activation energy of the reaction increase the particle energy decrease the effective collision frequency increase the rate of collision between particles

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Experiment Mass of copper (II) oxide/g

Volume of hydrogen peroxide /cm3

Concentration of hydrogen peroxide /mol dm-3

I 1 50 1.0


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II 1 100 0.5 Table 2

Two experiments were carried out to measure the rate of decomposition of hydrogen peroxide with copper(II) oxide as the catalyst , with conditions shown in the Table 2. Which of the following graphs shows volume of oxygen releases against time for Experiment 1 and Experiment 2 ?

A

B

C experiment II Gas experiment II Gas volume volume experiment I experiment I

time time D experiment I Gas experiment I Gas volume volume experiment II experiment II

time time

Total gas volume /cm3 v v/2-

time/s 0 10 20 30 40 Figure 418 Figure 4 shows the graph of total volume of gas against time for the reaction

between marble and dilute hydrochloric acid. From the graph, it can be deduced thatABCD

the rate of reaction at 10th second is lower than the rate at the 20th secondtotal volume of gas collected for the first 20 second is v/2 cm3

total volume of the gas collected in this experiment is v cm3

the maximum rate of gas released is at the 40th second 19 Among the acids below, which will give the highest initial rate of reaction when 1 g

of calcium carbonate powder was added to it ?ABCD

50.0 cm3 0.1 mol dm-3 nitric acid 50.0 cm3 0.1 mol dm-3 sulphuric acid50.0 cm3 0.1 mol dm-3 ethanoic acid100.0 cm3 0.1 mol dm-3 hydrochloric acid

20 The reactions between hydrochloric acid and zinc produces hydrogen gas. The reaction is completed in 50 seconds and the maximum volume of gas produced is 25 cm3 .


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What is the average rate of the reaction?

A 0.5 cm3 s-1

B 1.0 cm3 s-1

C 2.0 cm3 s-1

D 4.0 cm3 s-1

Reinforce Exercise for Structural Questions and Essay Questions.

1. The rate of reaction is affected by several factors. One of the factors is the size of particles.

(a) Explain the above statement based on the size of the particles.[2 marks]

(b) A student carried out three experiments to investigate the effects of the factors influencing the rate of reaction. Table 1 shows the results of the experiments.

(i) Write the chemical equation for the reaction between magnesium and hydrochloric acid. Calculate the maximum volume of hydrogen gas produced.

[ Relative atomic mass: Mg,24; molar mass volume: 24 dm3 mol-1 at room condition][4 marks]

(ii) Sketch the graphs for the volume of hydrogen gas against time for Experiment I, II and III on the same axes.

[3 marks]

(iii) Calculate the average rate of reaction for Experiment I, II and III in cm3 s-1.


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One kilogramme of meat, cut into big pieces, takes a longer time to cook compared to one kilogram of meat cut into smaller pieces.

[3 marks]

(iv) Compare the rates of reaction between Experiment I and Experiment II, and between Experiment II and Experiment III.

With reference to collision theory, explain why there are differences in the rates of reaction in the experiments.

[8 marks]

2. An experiment was conducted to find out the effects of temperature on the rate of reaction. 50cm3 of sodium thiosulphate solution 0.05 mol dm-3 at 30oC was put into a 250cm3 conical flask. Then the conical flask was placed on an ‘X’ sign on a piece of white paper.

10cm3 of hydrochloric acid 1.0 mol dm-3 was added to the sodium thiosulphate solution and shaken. At the same time, the stop watch was started. The stop watch was stopped as soon as the ‘X’ sign was no longer visible.

The same steps of the experiment were repeated for sodium thiosulphate solution which was heated to 35oC, 40oC, 45oC and 50oC.

Figure 1 shows the readings of the stop watch for each of the reaction at different temperatures.


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(a) Record the time for each reaction in the spaces provided in Figure 1.

(b) Construct a table and record temperature, time and 1/time for this experiment.

(c) (i) Draw a graph of temperature against 1/time on the graph paper.

(ii) Based on the graph in c(i) , state the relationship between the rate of reaction and temperature.

(d) Predict the time taken as soon as the sign ‘X’ to be not longer visible if this experiment is repeated at 55oC.

(e)(i) State the variables involved in this experiment.

Manipulated variable:

Responding variable:

Constant variable:

(ii) State how you would manipulate one variable while keeping the other variables constant.

(f) State the hypothesis for this experiment.

(g) From the above experiment, the student found a relationship between temperature and rate of reaction. The same situation can be applied in our daily lives, for example, keeping food that is easily spoiled in the refrigerator.

Using your knowledge of chemistry, state the relationship between temperature and the rate at which food turns bad.


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3(a) Food stored in a refrigerator last longer than food stored in a kitchen cabinet. Explain why.

[4 marks]

(b) A group of pupils carried out three experiments to investigate the factors affecting the rate of a reaction.Table 7 shows information about the reactants and the temperature used in each experiment.

Experiment Reactants Temperature /oCI Excess calcium carbonate chips and 30 cm3 of 0.5

mod dm-3 hydrochloric acid30

II Excess calcium carbonate chips and 30 cm3 of 0.5 mod dm-3 hydrochloric acid

40

III Excess calcium carbonate powder and 30 cm3 of 0.5 mod dm-3 hydrochloric acid

40

Table 7.

Graph 7 shows the results of these experiments.

(i) Calculate the average rate of reaction for experiment I. [2

marks]

(ii) Based on Table 7 and graph 7, compare the rate of reaction between: Experiment I and Experiment II Experiment II and Experiment III

In each case explain the difference in rate of reaction with reference to the collision theory.

[ 10 marks]


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(iii) The chemical equation below shows the reaction between calcium carbonate and hydrochloric acid.

CaCO3 + 2HCl CaCl2 + CO2 + H2O

Given that the relative atomic mass of C=12, O=16, Ca=40 and the molar volume of any gas is 24 cm3 mol-1 at room temperature and pressure.

Calculate the maximum volume of carbon dioxide gas produced in Experiment II. [4 marks]

4. Diagram 6 shows two experiments to investigate one factor that influences the rate of a

reaction.


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(a) What is the factor that influences the rate of reaction in both experiments?[1 mark]

(b) The reaction in the experiment is represented by the following equation:

CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)

(i) Among the products stated in the equation, which is the most suitable to be chosen to determine the rate of reaction?

[1 mark](ii) State one reason for choosing the product in 6(b)(i)

[1 mark](c) State two controlled variables in both experiments.

1.

2.[2 marks]

(d) The results for both experiments are represented by graph 6.


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Quantity of product

Time

Experiment I

Experiment II

Key:

x

Based on Graph 6:

(i) Experiment II has a higher rate of reaction. How does the graph show this?

[1 mark]

(ii) What has happened to the reactants at time x?

[1 mark]


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10 rate of reaction

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