Module 7 Rate of Reactions

8/6/2019 Module 7 Rate of Reactions

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CHAPTER : RATE OF REACTIONS

1.Concept Map

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

MODULE 7

RATE OF

REACTIONS


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2. Rate of reaction

(a) Rate of reaction is the sat 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 Reaction

1 Corrosion of iron nail slow

2 Striking a match

3 Photosynthesis

4 Neutralization

5 Acid with reactive metal

6 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

(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

Rate of reaction

..


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(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 changeTime 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

(ii) If time taken for 5.0 gram of magnesium ribbon reacts completely with dilutehydrochloric 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.

takentime

quantityselectedinchangereactionofRate =

takentime

gashydrogenofvolumeinincreasereactionofRate =

takentime

magnesiumofmassindecreasereactionofRate =


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For the reaction bellow

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

Sketch the graph for:

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

(e) Rate of reaction can be measured as average rate of reaction or the rate of reactionat a particular given time.

(f) Average rate of reaction is the avalue 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 reactionwhere gas is given off

Concentration ofHCl / mol dm-3

time

1, s-1

Concentration ofHCl / moldm-3 Mass ofZnCO3/ g

Time/s Time/s

Concentration ofZnCl

2/ mol dm-3

Volume of CO2

gas / cm3

Time/s Time/s


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Activity:

Table bellow shows the burette reading of hydrogen gas collected at different time intervalswhen magnesium ribbon react with hydrochloric acid

Time/s 0 30 60 90 120 150 180 210 240 270 300

Burettereading/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 gascollected/cm3

(a) Calculate the volume of gas collected

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

Rate of reaction at time t1 =

EFoflength

DFoflengthcm3s-1

Gradient of the tangent atany 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 ofgas/cm3

E

F

D

t1

M


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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


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(iii) the overall average rate of reaction

(iv) the rate of reaction at 1 minute

(v) the rate of reaction at 3 minutes

(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 andhydrochloric acid.

4. Factors affecting rate of reaction

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


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(a) For a fixed mass of solid reactant, the smaller the size of the reactant thehigher 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 withhydrochloric acid of the same volume and concentration.

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

Problem statement:

Hypothesis:

Variables:

(i) manipulated variable: .

(ii) responding variable:.

(iii) fixed variable:

Materials:

Apparatus:


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(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?

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

5. Write a balanced chemical equation for the reaction between calcium carbonate andhydrochloric 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 gascollected the same? Explain your answer.

8. If the marble chips used in the experiment is in excess, what is the maximum totalvolume 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:

Variables:




Materials:

Apparatus:


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Procedure:(Diagram)

Results:

Experiment 1 2 3 4 5

Volume of 0.2moldm-3 sodiumthiosulphate solution, V1 cm

3 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 acidadded/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 sodiumthiosulphate solution used/moldm-3

Time taken/s 16 20 27 41 83

1/time , s-1

1. Plot the graph of concentration of sodium thiosulphate solution used against timetaken 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.


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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 sodiumthiosulphate 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 acidin this experiment, predict the rate of reaction and explain your answer.

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 reactionbetween thiosulphate solution and dilute hydrochloric acid.

Problem statement:

Hypothesis:

Variables:


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Materials:

Apparatus:

Procedure:(Diagram)

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 withtemperature.


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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 foreach experiment?

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

Conclusion:

IVEffect 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

The a of products formed remain unchanged

with or without the catalyst

Time/s

Volume ofhydrogenreleased/cm3

Without catalyst

With catalyst


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Only a small amount of catalyst is needed to achieve

a bchange 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 fordecomposition of hydrogen peroxide solution.

Problem statement:

Hypothesis:

Variables:

(i) manipulated variable: ..

(ii) responding variable:



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Test tube Observation

A

B

Discussion:

1. What is the effect of manganese(IV) oxide on the decomposition of hydrogenperoxide 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 tubeB?

Conclusion:

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

Problem statement:

Hypothesis:

Variables:

(i) manipulated variable: ..

(ii) responding variable:


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Apparatus:

Materials:

Procedure:

.


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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

Burettereading/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 ofgas 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

Burettereading/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

Volume of

gas cm3

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

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

(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?


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5. If both experiments are allowed to proceed until completion, is the total volume ofgas

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. Catalystis specific in its action and only a small amount is required in a chemical reaction.

Industrialprocess

Productproduced

Equation Catalyst

Haber Process

Contact Process

Ostwald Process

Hydrogenation ofvegetable oil

Cracking ofpetroleum


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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 temperature

Experiment 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 + MnO2Experiment 2 50 cm3 of 1.0 moldm-3 NaOCl + MnO2

Volume of

oxygen/cm3

Time/s

Volume of

oxygen/cm3

Time/s


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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 atroom temperature

Explain your answer

8.Collision Theory

(a) For a chemical reaction to occur, the particles of the reactants must collide with eachother. 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

Volume of

hydrogen/cm3

Time/s


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

(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 ofreactant per unit volume.

The frequency of collision of particles of reactant increases.

The frequency of effective collision increases.


3. The effect of increase in temperature of reaction

o By increasing the temperature of the reactant

o 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 increases

o The rate of reaction increases.

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

Energy

Reactant

Product

Ea

Energy

Reactant

ProductEa


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

The frequency of effective collision 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 reactantsAre in the gaseous state.

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

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

o the number of particles per unit volume increases.

o The frequency of collision among the reactant particles increases

o The frequency of effective collision increases

o Hence the rate of reaction increases.

Activity:

1. Complete the following table:

Experiment Factor affect the Sketch of graph Explain using collision theory

Energy

Reactant

Product

Ea

Ea

Energy

Reactant

Product

Ea

Ea


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rate of reaction

Two set of experimentis carry out betweenmarble chip andhydrochloric acid:

Exp I: Excess of zincpowder and 50 cm3 of0.5 moldm-3

hydrochloric acidExp II: Excess of zincgranule and 50 cm3 of0.5 moldm-3

hydrochloric acid

The rate of reaction in exp Iis than exp II

The gradient of the curve forexp I is . than

exp II Zinc powder has .

total surface area

Frequency of collision ofzinc 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.

Volume of gas /cm3

Time, s


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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 ofcolour 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 chlorinemolecules.

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

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 isdecomposed completely ?[1 mole of gas occupies 24 dm3 at room condition;Avogadros constant : 6 X 1023 mol-1]

I 2 moles of waterII 12 dm3 of oxygen gasIII 3 X 1023 of oxygen molecules

2H2O

2(aq)2H

2O

(l)+ O

2(g)

2Fe2+ + Cl2 2Fe3+ + 2Cl

Green Brown


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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 andhydrochloric acid to produce carbon dioxide gas.

Experiment Substances

I Excess marble and 50.0 cm3 of 2 mol dm-3 hydrochloric acid

II Excess marble and 100.0cm3 of 1 mol dm-3 hydrochloric acid

A C

B D

6 The reaction between hydrochloric acid and zinc produces hydrogen gas. Thereaction is complete in 50 seconds and the maximum volume of gas produced is25 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.

Volume of

CO2/cm3

Volume of

CO2/cm3

Volume of

CO2/cm3

Volume of

CO2/cm3

Time/s Time/s

Time/s Time/s

I

I

I

I

II

II

II

II

Energy


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

If the experiment is repeated using another solution, which solution will producecurve 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 intemperature on the reactant particles?

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

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

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 zincpowder?

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.

Volume ofoxygen

gas/cm3

Time/s

P

Q


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14 Which of the following mixture of limestone and 50 cm3 hydrochloric acid will givethe 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 acidicpotassium manganate (VII) . If excess of acidic potassium manganate (VII) wasused, the rate of reaction can be determined by theAB

CD

time manganese ion producedtime to decolourised the potassium manganate (VII) solution

mass 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 catalystwill

AB

CD

decrease the activation energy of the reactionincrease the particle energy

decrease the effective collision frequencyincrease the rate of collision between particles17

Experiment Mass of copper (II)oxide/g

Volume of hydrogenperoxide /cm3

Concentration ofhydrogen peroxide /moldm-3

I 1 50 1.0

II 1 100 0.5

Table 2Two experiments were carried out to measure the rate of decomposition ofhydrogen peroxide with copper(II) oxide as the catalyst , with conditions shown

in the Table 2. Which of the following graphs shows volume of oxygen releasesagainst time for Experiment 1 and Experiment 2 ?

A

B

C experiment IIGas experiment II Gas

volume volumeexperiment I experiment I

time timeD experiment I

Gas experiment I Gasvolume volume

experiment II experiment II


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time time

Total gasvolume /cm3 v

v/2-

time/s0 10 20 30 40

Diagram 4

18 Diagram 4 shows the graph of total volume of gas against time for the reactionbetween marble and dilute hydrochloric acid. From the graph, it can bededuced that

ABCD

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/2cm3

total volume of the gas collected in this experiment is vcm3

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 acid50.0 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. Thereaction is completed in 50 seconds and the maximum volume of gas produced is25 cm3 .

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 ofparticles.

One kilogramme of meat, cut into big pieces, takes a longer time to

cook compared to one kilogram of meat cut into smaller pieces.


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(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 thefactors influencing the rate of reaction. Table 1 shows the results of the

experiments.

(i) Write the chemical equation for the reaction between magnesium andhydrochloric acid. Calculate the maximum volume of hydrogen gas produced.[ Relative atomic mass: Mg,24; molar mass volume: 24 dm3 mol-1 at roomcondition]

[4 marks]

(ii) Sketch the graphs for the volume of hydrogen gas against time forExperiment 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.[3 marks]

(iv) Compare the rates of reaction between Experiment I and Experiment II, andbetween Experiment II and Experiment III.With reference to collision theory, explain why there are differences in therates of reaction in the experiments.

[8 marks]

2. An experiment was conducted to find out the effects of temperature on the rate ofreaction. 50cm3 of sodium thiosulphate solution 0.05 mol dm-3 at 30oC was put into a250cm3 conical flask. Then the conical flask was placed on an X sign on a piece ofwhite paper.10cm3 of hydrochloric acid 1.0 mol dm-3 was added to the sodium thiosulphatesolution and shaken. At the same time, the stop watch was started. The stop watchwas stopped as soon as the X sign was no longer visible.


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

(f) State the hypothesis for this experiment.

(g) From the above experiment, the student found a relationship betweentemperature and rate of reaction. The same situation can be applied in ourdaily lives, for example, keeping food that is easily spoiled in the refrigerator.Using your knowledge of chemistry, state the relationship betweentemperature and the rate at which food turns bad.

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 ineach experiment.

Experiment Reactants Temperature /oC

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

30

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

40

III Excess calcium carbonate powder and 30 cm3 of0.5 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]


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(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 tothe collision theory.[ 10 marks]

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

CaCO3 + 2HCl CaCl2 + CO2 + H2O

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

Calculate the maximum volume of carbon dioxide gas produced inExperiment II.

[4 marks]

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


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a reaction.

(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 mostsuitable 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.


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2.[2 marks]

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

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]

Quantityof product

Time

Experiment I

Experiment II

Key:

x

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Module 7 Rate of Reactions

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