Page 1

Rate of Reaction 1

by Ricky Tsui

Common laboratory techniques for the reaction rate measurement

Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

H2(g) very light gas

CO2(g) heavier gas

2 Volume of gas produced against time

CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) Loss in mass against time

Pressure change against time

Advantage of data-logger: 1. More accurate / sensitive 2. Experimental result in form of graph can be obtained immediately [05CE/10]

3

CH3COOCH2CH3(l) + NaOH(aq)  CH3COONa(aq) + CH3CH2OH(aq) (standard solution)

MnO4-(aq): purple;

4

Mn2+(aq): colorless

2MnO4-(aq) + 5C2O42-(aq) + 16H+(aq)  2Mn2+(aq) + 8H2O(l) + 10CO2(g) Concentration of MnO4-(aq) remained against time

Concentration of NaOH(aq) remained against time

quenched reaction mixture (NaOH(aq)) + phenolphthalein colorimeter (色度計)

S2O32-(aq) + 2H+(aq) SO2(g) + H2O(l) + S(s) to ‘stop’ a reaction

5

Common quenching techniques: 1. Cool by ice-bath 2. Infinite dilution by adding water 3. Removing catalyst 4. Removing one of the reactants

Time required for the “X” to be disappeared

Ch 20 – Rate of Chemical Reaction

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Page 1


Rate of Reaction

by Ricky Tsui

Rate of a reaction = = Class practice: 1.

𝐚𝐦𝐨𝐮𝐧𝐭 𝐨𝐟 𝐩𝐫𝐨𝐝𝐮𝐜𝐭 𝐟𝐨𝐫𝐦𝐞𝐝 𝐭𝐢𝐦𝐞 𝐭𝐚𝐤𝐞𝐧 𝐚𝐦𝐨𝐮𝐧𝐭 𝐨𝐟 𝐫𝐞𝐚𝐜𝐭𝐚𝐧𝐭 𝐮𝐬𝐞𝐝 𝐭𝐢𝐦𝐞 𝐭𝐚𝐤𝐞𝐧

2.

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

by Ricky Tsui

Chemical reaction

How to follow the progress of a reaction?

Unit for reaction rate

Mg(s) + HCl(aq)

CaCO3(s) + HCl(aq)

CH3COOCH2CH3(l) + NaOH(aq) 

MnO4-(aq) +

C2O42-(aq) +

H+(aq) 

S2O32-(aq) + H+(aq) 

Br2(aq) + HCOOH(aq) 

Class practice (p.2):

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction 1.

by Ricky Tsui

In which of the following reactions the rate CANNOT be measured by the set-up shown?

collected gas

gas syringe

2. Which of the following methods can monitor the rate of the reaction between Mg ribbon and HCl? (1) Measuring the change in mass of the reaction mixture (2) Measuring the change in colour intensity of the reaction mixture (3) Measuring the change in pressure of the reaction system

dilute hydrochloric acid

magnesium ribbon A. B. C. D.

ZnCO3 + HCl Zn + H2SO4 ZnO + HNO3 Zn + CH3COOH

3. A student is monitoring the progress of a chemical reaction by measuring the change in mass of the reaction mixture. The set-up is shown below:

A. B. C. D.

4. Which of the following reactions CANNOT be followed by using the method of measuring the change in pressure of a gas? A. B. C. D.

X hydrochloric acid

(1) only (2) only (1) and (3) only (2) and (3) only

Na2CO3 + HCl Zn + CH3COOH Na2SO3 + CH3COOH Zn + HCl

Y

electronic balance

Which of the following combinations is correct? X Y Cotton wool Magnesium A. plug carbonate B. Rubber plug Magnesium chloride Cotton wool C. Magnesium sulphate plug Magnesium D. Rubber plug hydroxide

Learn more about the titrimetric method

[I2(aq)] can be found by titrating against standard S2O32-(aq) using starch as indicator (dark blue to colorless)

I2(aq) + 2S2O32-(aq)  S4O62-(aq) + 2I ‾(aq)

[H2O2(aq)] can be found by titrating against standard MnO4-(aq) (indicator is not necessary, end-point: very pale pink) (see [06AL/paperII/4(a)(i)/4 marks])

2MnO4-(aq) + 5H2O2(aq) + 6H+(aq)  2Mn2+(aq) + 5O2(g) + 8H2O(l)

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction 5. Which of the following statements about the reaction between ethyl ethanoate and dilute sodium hydroxide solution is INCORRECT? A.

The concentration of a reactant at regular time intervals can be determined by titrimetric analysis. B. Ethanol is formed in the reaction. C. The reaction can be quenched with ice water. D. This reaction is regarded as esterification.

7. In order to follow the progress of the reaction, HCOOCH3(aq) + NaOH(aq)  HCOONa+(aq) + CH3OH(aq) Which of the following techniques can be used? (1) Titrimetric analysis (2) Colorimetric analysis (3) Measuring the loss of mass of the reaction mixture A. B. C. D.

(1) only (2) only (1) and (3) only (2) and (3) only

9. Which of the following methods can be used to determine the reaction rate of the following reaction? Cr2O72(aq) + 14H+(aq) + 3C2O42(aq)  6CO2(g) + 7H2O(l) + 2Cr3+(aq) (1) Measuring volume of CO2 formed (2) Measuring time for pH change (3) Measuring time for the colour of the solution to change from orange to green A. B. C. D.

(1) and (2) only (1) and (3) only (2) and (3) only (1), (2) and (3)

by Ricky Tsui

6. What is/are the advantage(s) of using titrimetric analysis to follow the progress of a reaction? (1) Only simple apparatus like pipette is required. (2) The reaction does not need to be quenched. (3) There is a continuous monitoring of the progress of reaction. A. B. C. D.

(1) only (2) only (1) and (3) only (2) and (3) only

8. 2MnO4(aq) + 5H2O2(aq) + 6H+(aq)  2Mn2+(aq) + 8H2O(l) + 5O2(g) Which of the following methods is/are possible for monitoring the progress of the above reaction? (1) Titrimetric analysis (2) Measuring the change in colour intensity by colorimetry (3) Measuring the change in volume of gas A. B. C. D.

(1) and (2) only (1) and (3) only (2) and (3) only (1), (2) and (3)

10. In order to follow the progress of the reaction, Br2(aq) + HCOOH(aq)  2Br(aq) + 2H+(aq) + CO2(g) Which of the following techniques can be used? (1) Measuring the volume of gas produced (2) Measuring the loss of mass of the reaction mixture (3) Colorimetry A. B. C. D.

(1) and (2) only (1) and (3) only (2) and (3) only (1), (2) and (3)

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction 11. The reaction rate of which of the following reactions can be measured using a colorimeter? A. B. C. D.

Dissolving eggshells in sulphuric acid solution The reaction of sulphur dioxide and bromine water The reaction of ethyl propanoate and sodium hydroxide The reaction of silver and nitric acid

by Ricky Tsui

12. Concerning the method used to study the progress of a chemical reaction between sodium thiosulphate and hydrochloric acid by measuring the change in transmittance of light through the reaction mixture, which of the following statements is correct? A.

B. C.

D.

The transmittance of light through the solution is affected by the formation of sulphur dioxide. A data-logger is required in this method. The rate of the reaction is directly proportional to the time taken for the ‘blot out’ of the cross. The cross should be seen from a position immediately above it.

13. Which of the following shows the correct sequence of results of measuring rate of reaction between sodium thiosulphate solution and dilute hydrochloric acid? (The diagrams show the top view of the solution in a beaker putting on top of a marked cross.) A .

B .

C .

D .

14. Which of the following methods can be used to quench a reaction? (1) Cooling the reaction mixture slowly (2) Removing one of the reactants (3) Diluting the reaction mixture with cold water A. B. C. D.

(1) and (2) only (1) and (3) only (2) and (3) only (1), (2) and (3)

15. Which of the following methods can be used to quench a reaction? (1) Diluting the reaction mixture (2) Cooling the reaction mixture (3) Removing the reactant (4) Removing the product A. B. C. D.

(1), (2) and (3) (1), (2) and (4) (1), (3) and (4) (2), (3) and (4)

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

by Ricky Tsui

Rate curves and its interpretation

1 Experimental data 2

can find out… 3

Reaction rate A

a typical rate curve B2

C

B

C

(平均

Average 的) reaction rate

TOTAL amount of product TOTAL time taken for reaction

B

B1

(瞬間

Instantaneous 的) reaction rate

Step 1: draw a tangent at the point Step 2: find the slope of the tangent drawn

A

Initial

(起初

reaction rate的)Slope of the steepest part of curve

A

= (10-0) / (10-0) = 1 cm3/s Initial rate is useful for finding out (1) the order of reaction and (2) the value of rate constant! (We will learn it in an elective topic – Industrial Chemistry)

C

B

Initial reaction rate 16. At = =

Instantaneous reaction rate 17. B1 B2 At = cm3/s = Drawing a tangent line is a challenging task. In most cases, tangent line is provided. Compare the instantaneous rate at A, B1 and B2, any implication?

Average reaction rate

18. = = Reminder: Don’t overlook that the total time taken for the reaction is 120 s but not 180 s.

Ch 20 – Rate of Chemical Reaction

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Page 7


Rate of Reaction

by Ricky Tsui

Class practice:

Ch 20 – Rate of Chemical Reaction

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Page 8


Rate of Reaction

by Ricky Tsui

19. Based on the definition for rate of reaction, which of the following is a unit of reaction rate? A. B. C. D.

mol dm3 mol s2 dm3 min3 mol dm3 min1

20. Which of the following is NOT a unit of chemical reaction rate? A. B. C. D.

s mol1 cm3 s1 g min1 mol dm3 s1

21. Which of the following diagrams shows a correct rate curve for a chemical reaction? A.

B.

Amount of product in the reaction

Time

Time

C.

Amount of product in the reaction

D.

Amount of product in the reaction

Amount of product in the reaction

Time

Time

22. The experiment shown in the diagram was set up and the syringe reading was noted at intervals. rubber connecting tubing

23. The graph shows how the total volume of carbon dioxide produced by the reaction between dilute nitric acid and excess calcium carbonate varied with time. Total volume of carbon dioxide produced

gas syringe

dilute HCl MgCO3(s)

A graph of the syringe readings against time was plotted. Which of the following curves would be obtained?

P

Q

Time

Which of the following statements about section PQ of the curve is correct? A. The speed of reaction is at maximum. B. All calcium carbonate has reacted.

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

by Ricky Tsui

C. D.

Volume of gas

No more carbon dioxide is being produced. The concentration of the acid is increasing.

A B C

D Time

24. When 50 cm3 of 0.20 M hydrochloric acid was mixed with excess sodium thiosulphate solution, the following reaction occurred. S2O32(aq) + 2H+(aq)  SO2(aq) + H2O(l) + S(s) 0.161 g of S was produced in 2 minutes. What is the average rate of production of S? A. 8.05 × 102 g s1 B. 1.34 × 103 g s1 C. 0.417 cm3 s1 D. 1.67 × 103 M s1

25. 5 g of calcium carbonate takes 250 s to react with the solution of hydrochloric acid completely. What is the average reaction rate of the reaction?

26. When 10 cm3 of 1.0 M acidified potassium permanganate is mixed with excess ethanedioate, the purple colour of the solution disappears after 40 s. Calculate the average reaction rate of the reaction.

27. A chemical reaction completed in 10 minutes and released 0.16 g of oxygen gas. What is the average rate of this reaction?

A. B. C. D.

0 M s 1 0.025 M s1 0.050 M s1 40 M s1

28. Consider the esterification between ethanol and ethanoic acid in the presence of an acid catalyst. The concentration of ethyl ethanoate builds up to 0.68 mol dm3 in 2 minutes. Calculate the average rate of the reaction. A. B. C. D.

0.68 mol dm3 min1 0.34 mol dm3 min1 0.68 mol min1 0.34 mol min1

A. B. C. D.

A. B. C. D.

0.16 mol s1 0.020 mol s1 2.0 × 104 mol s1 2.0 × 105 mol s1

8.33 × 9.33 × 5.00 × 8.00 ×

106 mol s1 105 mol s1 104 mol s1 103 mol s1

29. Combustion of methane gives carbon dioxide as one of the products. CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) The concentration of carbon dioxide increases from 0 to 2 × 102 mol dm3 in 0.01 seconds. What is the average rate of decrease of O2(g) concentration? A. B. C. D.

0.02 mol dm3 s1 0.04 mol dm3 s1 2 mol dm3 s1 4 mol dm3 s1

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction 30. Instantaneous rate can be obtained from a concentration-time graph. Which of the following methods is correct?

31. A reaction follows the concentration-time diagram. Which of the following values is closest to the instantaneous rate for this reaction at the 20th second?

Multiplying the concentration by time Measuring the slope of the graph at that Measuring the area under the graph Dividing the concentration by time

Concentration (M)

A. B. instant C. D.

by Ricky Tsui

Time (s)

A. B. C. D.

5 × 103 M s1 5 × 103 M s1 2 × 103 M s1 2 × 103 M s1

Volume of hydrogen gas (cm3)

32. The following graph shows the volume of hydrogen gas produced against time.

Time of reaction (min)

Which of the following statements about the above graph is INCORRECT? A. The average rate of the reaction is about 7.25 cm3 min1. B. The average rate between t = 1 min and t = 3 min is about 13.5 cm3 min1. C. The instantaneous rate at t = 1 min is about 23.0 cm3 min1. D. The instantaneous rate at t = 2 min is about 21.0 cm3 min1.

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

by Ricky Tsui

33. Which of the following can be shown by a rate curve?

34. Which of the following statements concerning a rate curve is/are true?

(1) Instantaneous rate of a reaction (2) Average rate of a reaction (3) Amount of reactants/products at a particular time A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3)

(1) The initial rate must be the fastest. (2) If the slope of the tangent equals zero, then the reaction stops. (3) The slope of the tangent must decrease from the largest value to zero. A. (1) only B. (2) only C. (1) and (3) only D. (2) and (3) only

35. The rate curve of the amount of carbon dioxide produced when an acid reacts with a carbonate is plotted. When is the rate of the reaction the fastest? A. B. C. D.

The graph is the steepest. The graph is at 45 to the horizontal. The graph is half finished. The graph is horizontal.

[12DSE/paper1/1mark] 36. In an experiment, 50 cm3 of 2.0M HCl(aq) was added to a conical flask containing 2.0 g of zinc powder. The curve in the graph below shows the volume, measured at room temperature and pressure, of the hydrogen gas liberated in the first few minutes of the experiment. The dotted line in the graph is the tangent to the curve at the start of the reaction. The ‘initial rate’ of a reaction is defined as the instantaneous rate at the start of the reaction. With reference to the graph above, calculate the initial rate of the reaction with respect to the volume of hydrogen gas liberated.

Ch 20 – Rate of Chemical Reaction

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Page 12


Rate of Reaction Rate curve (example)

by Ricky Tsui

interpretation

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

time slope of curve rate of reaction

explanation

37.

Interpret the following graph showing the progress of a a reaction between HCl(aq) and Mg(s).

Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

__________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ Ch 20 – Rate of Chemical Reaction

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Page 13


Rate of Reaction

by Ricky Tsui

[09CE/10(b)(i)/3 marks] 38.

Explain why the respective rates of decomposition of hydrogen peroxide differ at points A, B and C on the curve.

Ch 20 – Rate of Chemical Reaction

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Page 14


Rate of Reaction

by Ricky Tsui

Factors affecting rate of reaction e.g. H2(g) + Cl2(g) ďƒ 2HCl(g)

3 1

collision

Product is formed

Chemical reaction may occur

faster

2

more effective collision chance within a certain time

Which case (A1 or A2) will have a faster reaction rate?

Ans: _________

What is the factor causing this difference in reaction rate?

Ans: _____________

Higher temperature

Lower temperature

Which case (B1 or B2) will have a faster reaction rate?

Ans: _________

Why? Ans: ____________________________________________________ What is the factor causing this difference in reaction rate?

Ans: _____________

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

by Ricky Tsui

Example: Which acid will give bubbles in a faster rate with Mg? Explain. 1M HCl or 1M CH3COOH? 1M HCl will give bubbles at a faster rate.

1M HCl or 1M H2SO4? 1M H2SO4 will give bubbles at a faster rate.

Because HCl is a strong acid but CH3COOH is a weak

Because H2SO4 is a dibasic acid but HCl is a

acid, HCl can completely ionized into water.

monobasic acid,

HCl contains higher concentration of hydrogen

H2SO4 contains higher concentration of

ions than CH3COOH.

hydrogen ions than HCl.

More effective collision chance within a certain

More effective collision chance within a

time between HCl molecule and Mg.

certain time between H2SO4 molecule and Mg.

Class practice: Which acid will give bubbles in a faster rate with Mg? Explain.

1.

1M carbonic acid or 1M HNO3? ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________

2.

0.1M HNO3 or 0.1M H2SO4?

____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

by Ricky Tsui

[H+(aq)] from an acid is affected by ‌ 39.

[09CE/MC35,36] Directions: Questions 35 and 36 refer to the following information. The table below shows how solutions X and Y are respectively made from two monobasic acids A and B. Solution X

Solution Y

40 cm3 of 0.2 M acid A + 10 cm3 of distilled water

20 cm3 of 0.4 M acid B + 30 cm3 of distilled water

40. What is the concentration of acid A in solution X? A. B. C. D.

0.2 M 0.16 M 0.01 M 0.008 M

41. Two identical zinc strips are added to solutions X and Y. The diagrams below show how gas bubbles are given out when the zinc strips are just added to the solutions.

Which of the following deductions is correct? A. B. C. D.

Acid A is weaker than acid B. Acid B is weaker than acid A. The concentration of acid A in solution X is higher than that of acid B in solution Y. The concentration of acid B in solution Y is higher than that of acid A in solution X.

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

by Ricky Tsui

[09CE/MC43] 42. Beaker A contains 100 cm3 of 1 M HCl (aq), while beaker B contains 50 cm3 of 2 M HCl (aq). Equal mass of magnesium ribbons are added to the two beakers. Both magnesium ribbons disappear after reaction. Which of the following statements is/ are correct? (1) (2) (3)

The reactions occurring in both beakers have the same initial rate. Same volume of gas, measured at the same temperature and pressure, is given out in both beakers. Magnesium chloride solutions of the same concentration are produced in both beakers.

A. B. C. D.

(1) only (2) only (1) and (3) only (2) and (3) only

[08CE/MC39] 43. Consider the following information on two reactions involving magnesium ribbons of the same shape: Reacting mixture Reaction 1 1.5 g of Mg + 100 cm3 of 1 M HCl Reaction 2 1.5 g of Mg + 100 cm3 of 1 M H2SO4 Which of the following statements is correct? (Relative atomic mass : Mg = 24.3) A. B. C. D.

The magnesium reacts completely in Reaction 1. The sulphuric acid reacts completely in Reaction 2. The initial rates of Reaction 1 and Reaction 2 are the same. The initial rate of Reaction 1 is smaller than that of Reaction 2.

*[07CE/MC47] 44. A student pours two different acids respectively into two test tubes, each containing a piece of magnesium ribbon of the same mass, until the ribbons are completely covered by the acids. If she wishes to compare the relative strength of the acids by observing the initial rate of evolution of gas, which of the following items should be the same? (1) (2) (3)

volume of acids concentration of the acids basicity of the acids

A. B. C. D.

(1) and (2) only (1) and (3) only (2) and (3) only (1), (2) and (3)

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

by Ricky Tsui

[12DSE/paper1/2marks] 45. In an experiment, 50 cm3 of 2.0M HCl(aq) was added to a conical flask containing 2.0 g of zinc powder. The curve in the graph below shows the volume, measured at room temperature and pressure, of the hydrogen gas liberated in the first few minutes of the experiment. The dotted line in the graph is the tangent to the curve at the start of the reaction.

Explain qualitatively the effect on the initial rate of the reaction of replacing the 2.0M HCl(aq) with 2.0M H2SO4(aq).

Ch 20 – Rate of Chemical Reaction

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Page 19


Rate of Reaction

by Ricky Tsui

Factor 1 - initial concentration of reactant(s)

Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

Different initial concentrations are used

I. 0.5 M HCl II. 1.0 M HCl III. 1.5 M HCl IV. 2.0 M HCl

Predict the other three rate curves for different initial concentrations of HCl(aq) are used. (Hint: shapes of curves are similar):

III.

1.5 M HCl

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

by Ricky Tsui

Possible rate curves (1) if HCl(aq) is in excess Interpretation: If a _________ initial concentration of HCl(aq) is used, the initial rate of reaction will be _____________. Because the _____________ for ______________ _______________ is higher.

Possible rate curves (2)

if Mg(s) is in excess

If excess Mg(s) is used, all H+(aq) will be reacted to form H2(g). Provided that four HCl(aq) solutions are equal in volume, higher concentration one will have a larger no. of mole of H+(aq), and finally more H2(g) will be produced. Higher initial concentration of HCl(aq), Faster initial rate of reaction. 46. In the graphs below, curve (i) was obtained when 3 g of zinc granules was reacted with excess 2.0 M hydrochloric acid. Curves (ii) and (iii) were obtained after making changes to the acid. Curve (ii): Excess 1.0 M nitric acid Curve (iii): Excess 1.5 M sulphuric acid Which of the following graphs matches the rate curves (i), (ii) and (iii) correctly? A.

B.

C.

D.

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

by Ricky Tsui

Factor 2 - temperature

S2O32-(aq) + 2H+(aq) ďƒ SO2(g) + H2O(l) + S(s)

Explanation

47. An increase in temperature of the reactants increases the rate of reaction. Which of the following statements explains this situation correctly? A. Heat energy causes an increase in concentration of the reactants. B. Heat energy causes an increase in size of the molecules. C. Heat energy causes a decrease in energy required for the reaction to occur. D. Heat energy causes the reactant particles to move faster.

48. Which of the following statements correctly explains the effect of increase in temperature of reactants on reaction rate? A. Increase in temperature raises the potential energy of the reactant particles. B. Increase in temperature reduces the energy difference between the reactants and products. C. Increase in temperature raises the average kinetic energy of the reactant particles. D. Increase in temperature reduces the contribution from orientation factor.

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction 49. Arrange the following reaction rates in descending order. (1) Reaction between 3.0 g of magnesium granules and 1.0 M of CH3COOH at room temperature. (2) Reaction between 3.0 g of magnesium powder and 1.0 M of HCl at a warm water bath. (3) Reaction between 3.0 g of magnesium powder and 0.6 M of H2SO4 at a warm water bath. (4) Reaction between 2.0 g of magnesium granules and 0.9 M of CH3COOH at room temperature. A. (1) > (3) > (4) > (2) B. (2) > (3) > (4) > (1) C. (2) > (4) > (1) > (3) D. (3) > (2) > (1) > (4)

**51.

by Ricky Tsui

50. A chemical reaction takes place inside a glow stick. The higher the temperature, the brighter is the glow stick. Which of the following descriptions about the glowing time at a higher temperature is correct? A. Longer B. Shorter C. Unchanged D. Uncertain

Na2S2O3(aq) + H2SO4(aq)  Na2SO4(aq) + H2O(l) + SO2(g) + S(s)

Which of the following reactions has the shortest time for ‘blot out’ at room temperature and pressure? Na2S2O3 H2SO4 H2 O Volume Concentration Volume Concentration Volume (cm3) (cm3) (cm3) (mol dm3) (mol dm3) A. 5 0.15 10 0.15 0 B. 5 0.20 10 0.10 5 C. 10 0.10 10 0.10 0 D. 5 0.20 5 0.20 10 ##A A small increase in temperature often produces a large increase in the rate of a chemical reaction because it A. decreases the size of the reactant particles. B. increases the effectiveness of the collisions between the reactant molecules. C. decreases the number of collisions per second between the reactant molecules. D. decreases the volume of the solution, altering the concentrations of the reactants.

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

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[05CE/10(b)(iv)/2 marks] 52. An experiment was carried out to study the action of water on a tablet of the effervescent vitamin C using the set-up as shown below. The graph shows the results obtained in the experiment. Each tablet contains 1000 mg of vitamin C. Other ingredients: sodium hydrogencarbonate, citric acid, sugar and colourant cotton wool

conical flask 50 cm3 of cold water

vitamin C tablet Electronic balance with data-logger

Computer

Suggest ONE advantage of using a data-logger in this experiment.

The experiment was repeated using warm water instead of cold water. Sketch, on the same graph, the result that would be obtain in the repeated experiment. 168.24

mass of conical flask and its content/g

168.23 168.22 168.21 168.2 168.19 168.18 168.17 168.16 168.15 168.14 168.13 168.12 0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

time/s Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

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Factor 3 - contacting surface area

Total

contacting surface area between A(s) and B(aq)

=

Total

contacting surface area between A(s) and B(aq)

=

larger contacting surface area between reactants (粉狀)

chip form

What if powder form is used? (片狀) chip form

[10CE/MC44] 53.

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

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55. Consider the reaction between solid calcium carbonate and aqueous hydrochloric acid. Which of the following conditions can be increased to speed up the reaction? (1) Concentration of HCl (2) Surface area of the CaCO3 particles (3) Temperature A. (1) and (2) only B. (1) and (3) only C. (2) and (3) only D. (1), (2) and (3)

56. Which of the following is the reason for the fact that antacids have to be chewed before swallowing? A. A catalyst is added by saliva. B. The temperature of the antacid is increased. C. The surface area of the antacids is increased. D. The concentration of the antacids is increased.

57. Excess magnesium was added to a beaker of aqueous hydrochloric acid on a balance. A graph of the mass of the beaker and contents was plotted against time (curve 1).

Mass

54. Powdering a solid reactant can A. increase the chance of collision between reactant particles. B. reduce the energy required for reaction to occur. C. increase the concentration of the reactant. D. convert the reactant into a catalyst.

1 2 Time

Which of the following changes in the experiment could give curve 2? (1) The same mass of magnesium but in smaller pieces (2) The same volume of a more concentrated solution of hydrochloric acid (3) A lower temperature A. (1) only B. (2) only C. (1) and (3) only D. (2) and (3) only

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

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Factor 4 - presence of catalyst Catalyst is a substance that can speed up a chemical reaaction without changing its chemical nature. N2(g) + H2(g)

NH3(g)

Examples of use of catalyst: 1. Haber process: to prepare NH3(g) industrially, iron powder as catalyst, 450 oC, 250 atm N2(g) + 3H2(g)

2NH3(g)

Fe(s) as catalyst

2. Contact process: to prepare SO3(g) and

then convert to H2SO4(l) , vanadium (V) oxide as catalyst, 450oC, 1atm 2SO2(g) + O2(g)

2SO3(g)

3. Decomposition of H2O2(aq) with MnO2(s) as catalyst 4. Biological enzymes: enzyme from yeast for alcohol preparation (fermentation), amylase in saliva, etc.

catalyst Ea = minimum energy required to start a reaction

can provide an alternative reaction pathway with a lower Ea (activation energy)

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

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[09CE/10/9 marks] 58.

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction [06CE/MC44] 59. Which of the following statements concerning a catalyst are correct? (1) A catalyst can alter the rate of reaction. (2) The mass of a catalyst remains unchanged at the end of the reaction. (3) A catalyst should be in the same physical state as the reactants. A. B. C. D.

by Ricky Tsui

[04CE/MC19] 60. Which of the following conversions does NOT require a catalyst? A. B. C. D.

Fe2O3(s) → Fe(s) SO2(g) → SO3(g) NH3(g) → NO(g) CO(g) + NO(g) → CO2(g) + N2(g)

(1) and (2) only (1) and (3) only (2) and (3) only (1), (2) and (3)

[02CE/MC12] 61. Which of the following reactions does NOT require the use of a catalyst? A. conversion of ammonia to nitrogen monoxide B. hydration of ethane to give ethanol C. oxidation of ethanol to ethanoic acid D. fermentation of glucose to give ethanol

[00CE/MC10] 63. Manufacturing ammonia by Haber process involves the reversible reaction: N2(g) + 3H2(g) ⇌ 2NH3(g) Which of the following statements concerning the process is INCORRECT? A. The forward reaction can go to completion if iron powder is used as a catalyst. B. The optimum conditions for the process are 500oC and 200 atm. C. The raw materials are derived from air and water. D. The forward reaction and backward reaction occur simultaneously.

[02CE/MC42] 62. In which of the following is ammonia used? (1) the manufacture of nitric acid (2) the marking of fertilizers (3) the making of antiacids A. B. C. D.

(1) and (2) only (1) and (3) only (2) and (3) only (1), (2) and (3)

[00CE/MC21] 64. Which of the following processes requires a catalyst? A. preparation of ethyl ethanoate from ethanoic acid and ethanol B. conversion of sulphuric trioxide to concentrated sulphuric acid C. manufacture of chlorine bleach from brine D. reduction of iron(III) oxide to iron

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

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Challenging question 65. In the presence of manganese(IV) oxide (as a catalyst), 40 cm3 of hydrogen peroxide solution (H2O2(aq)) decomposed to give oxygen and water at room temperature and pressure. The volume of oxygen evolved with time are shown in the following graph:

(The volumes of oxygen are measured at room temperature and pressure.) a)

Suggest a method for measuring the volume of oxygen evolved.

b)

Write the equation for the decomposition of the hydrogen peroxide solution.

c)

From the graph, determine i) the total volume of oxygen liberated in the reaction; ii) the time required for the liberation of two third of the total volume of oxygen.

d)

Explain the shape of the graph by considering changes in the rates of reaction.

e)

Calculate the molarity of the original hydrogen peroxide solution. (Hints: 1 mole of oxygen occupies 24 000 cm3.)

f)

Sketch, on the graph above, the curves you would expect if the experiment was repeated in an identical manner except that i) ii)

g)

the temperature was 40 °C; 5 cm3 of less concentrated hydrogen peroxide solution was added to 40 cm3 of the original hydrogen peroxide solution before the experiment.

Draw a labelled diagram of the apparatus which could be used to dry and collect the oxygen evolved.

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction Answer: 1. C 2. C 3. A 4. C 5. D 6. A 11. B 13. D 13. B 14. C 15. A

by Ricky Tsui

7. A

8. D

9. D

10. D

16 – 17.

18.

19. D 20. A 21. C 22. B 23. C 24. B 25. C 26. B 27. A 28. B 29. D 30. B 31. B 32. D 33. D 34. B 35. A 36. 37. From 0-20s, the slope is the largest, the reaction rate is the fastest, because the concentration of HCl is the highest. From 20 to 100s, the slope is decreasing, the reaction rate is decreasing, because the concentration of HCl is decreasing. At 120s, slope is zero, reaction stops, because reactant (Mg or HCl) has been used up. 38.

39. D 40. B 41. A 42. B 43. D 44. C 45.

46. C 47. D 48. C 49. D 50. B 51. B

Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

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52.

53. B 54. A 55. D 56. C 57. B 58.

59. A 60. A 61. C 62. A 63. A 64. A 65. a) Use a gas syringe. b) 2H2O2(aq) ďƒ 2H2O(l) + O2(g) c) i) 30 cm3 ii) 1.4 min d) Slope of the curve represents the rate of decomposition of H2O2 which depends on its concentration. At the beginning, the slope is steepest. It is because the concentration of H2O2 is highest and thus the rate of reaction is fastest. As the reaction proceeds, the slope becomes less steep. It is because the concentration of H2O2 decreases and thus the rate of reaction slows down. Finally, the curve becomes horizontal. It is because all the H2O2 is used up, the rate of reaction becomes zero. Ch 20 – Rate of Chemical Reaction

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Rate of Reaction

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e) Volume of O2 evolved = 30 cm3 Number of moles of O2 = 30 / 24000 = 0.00125 mol According to the equation in (b), the mole ratio of H2O2 to O2 = 2: 1. ďƒ Number of moles of H2O2 = 0.00125 x 2 = 0.0025 mol Molarity of H2O2 = 0.0025 / (40/1000) = 0.0625 M f)

(When 5 cm3 of less concentrated hydrogen peroxide solutuion was added to the original hydrogen peroxide solution, the concentration of the resulting solution decreased while the amount of hydrogen peroxide increased) g)

Ch 20 – Rate of Chemical Reaction

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Topic 9 rate of reaction (part a)  
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