A Level Official Exam Material
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Unit 5: Transition Metals and
Organic Nitrogen Chemistry
Topic 11: Kinetics
For A Level students only
Q1. Iodine reacts with propanone under acid conditions.
The reaction is first order with respect to propanone, first order with respect to hydrogen ions and zero order with respect to iodine.
What are the units of the rate constant? (1)
A dm3 mol–1 s –1
B mol dm–3 s –1
C s –1
D mol–2 dm6 s –1
(Total for question = 1 mark)
Q2. A reactant Q is converted into two products. Which of these graphs shows that this reaction is first order with respect to Q?
A Graph 1
B Graph 2
C Graph 3
D Graph 4
(Total for question = 1 mark)
Q3. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
The rate equation for a reaction is rate = k[A]2 [B]0
The initial rate of reaction is 9.0 × 10−5 mol dm−3 s −1 when [A] = 0.30 mol dm−3 and [B] = 0.20 mol dm−3 .
What is the value of the rate constant in dm3 mol−1 s −1?
A 8.1 × 10−6
B 3.0 × 10−4
C 1.0 × 10−3
D 5.0 × 10−3
(Total for question = 1 mark)
Q4. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
The rate of the reaction between two compounds, Y and Z, was investigated.
The results are shown.
Use this space for any rough working.
Anything you write in this space will gain no credit.
(Total for question = 1 mark)
Q5. This question is about the kinetics of the reaction between nitrogen monoxide and oxygen.
The rate equation for the reaction is rate = k[NO]2 [O2] (a) Which statement is not correct? (1)
A the reaction is third order overall
B the units of the rate of the reaction are mol dm−3 s −1
C the rate of the reaction increases when the pressure is increased
D when the concentration of nitrogen monoxide doubles and the concentration of oxygen quadruples, the rate increases by a factor of 8
(b) What are the units of the rate constant, k, for this reaction? (1)
A dm9 mol−3 s −1
B mol3 dm−9 s −1
C mol2 dm−6 s −1
D dm6 mol−2 s −1
(c) An experiment was carried out using 1.10 × 10−2 mol dm−3 of oxygen and some nitrogen monoxide.
The numerical value of the initial rate and rate constant were:
• initial rate = 3.20 × 10−3
• rate constant, k = 1.70 × 103
What was the initial concentration, in mol dm−3 , of the nitrogen monoxide used in the experiment? (1)
A 1.31 × 10−2
B 1.71 × 10−4
C 2.02 × 10−3
D 4.50 × 10−2
(Total for question = 3 marks)
Q6. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
This question is about chromatography.
(a) A spot caused by an amino acid has moved 42 mm from the baseline of a paper chromatogram.
The Rf value for the amino acid under these conditions is 0.62.
What is the distance moved by the solvent? (1)
A 680 mm
B 68 mm
C 42 mm
D 26 mm (b)
In gas chromatography, GC, which of these would be the most suitable carrier gas? (1)
A argon
B hydrogen
C methane
D oxygen
(Total for question = 2 marks)
Q7. Answer the questions with a cross in the boxes you think are correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross . Propanone reacts with iodine in acidic solution.
(a) Which of the following is true? (1)
A the units for the rate constant are dm3 mol−1 s −1
B the reaction is a first order reaction overall
C the units for the rate are dm3 mol−1 s −1
D doubling the concentrations of propanone and of iodine quadruples the rate
(b) Which of the following is not true? (1)
A the reaction rate increases if the temperature is raised
B the rate constant increases if the temperature is raised
C the addition of a small amount of sodium hydroxide decreases the reaction rate
D the rate is unchanged when the hydrogen ion concentration is doubled
Use this space for any rough working.
Anything you write in this space will gain no credit.
(Total for question = 2 marks)
Q8. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
The equation shows the hydrolysis of a bromoalkane.
The rate equation is rate = k[RBr] RBr is most likely to be
A bromomethane
B 2-bromopropane
C 1-bromo-2-methylpropane
D 2-bromo-2-methylpropane
(Total for question = 1 mark)
Q9. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
Nitrogen monoxide and hydrogen react together to form nitrogen and water.
2NO + 2H2 → N2 + 2H2O
The steps in the mechanism of the reaction are
Which statement about the reaction is correct?
A Step 3 is the rate determining step and the overall order is 2
B Step 3 is the rate determining step and the overall order is 4
C Step 2 is the rate determining step and the overall order is 2
D Step 2 is the rate determining step and the overall order is 3
(Total for question = 1 mark)
Q10. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross . Propanone reacts with iodine in the presence of a catalyst of dilute hydrochloric acid.
The reaction occurs in aqueous solution.
CH3COCH3 + I2 → CH3COCH2I + HI
The rate equation for this reaction is rate = k[CH3COCH3][H+ ]
Which is a possible mechanism for the reaction?
Q11. The decomposition of benzenediazonium chloride is a first order reaction.
C6H5N2Cl + H2O → C6H5OH + N2 + HCl
The activation energy of this reaction was determined by measuring the rate constant at various temperatures.
(a) In an experiment at 333 K, the concentration of a sample of benzenediazonium chloride was measured at various times during its decomposition.
The results of this experiment are shown.
(iii) Calculate the rate constant, k, for the reaction at 333 K.
Include units in your answer.
Use the expression ln 2 = kt 1 ⁄2 (2) (b)
The experiment described in (a) was repeated for five temperatures and the data used to plot a graph for the Arrhenius equation in the form
(i) Use the rate constant that you have calculated in (a)(iii) to obtain data for a point on the graph for 333 K.
(2) (ii) Plot your data from
(b)(i) on the graph. (1)
(iii) Determine the gradient of the graph by drawing a best-fit line.
Include a sign and units in your answer. (3)
(iv) Use the gradient determined in (b)(iii) to calculate the activation energy for the decomposition of benzenediazonium chloride.
Include a sign and units with your answer. (3)
(Total for question = 15 marks)
Q12. A student investigated the kinetics of the reaction between bromate(V) ions and bromide ions in acidic conditions.
(a) In the first experiment, the student measured the initial rate of the reaction at five different concentrations of bromate(V) ions, BrO3-(aq).
In each case, the initial concentrations of bromide ions and hydrogen ions were constant and in large excess.
The results obtained are shown.
(b) In the second experiment, the student determined the initial rates of the same reaction starting with different concentrations of the reactants.
(i) Use these results and your answer to (a) to deduce the orders with respect to Br– ions and H+ ions. (2)
Br– ions .............................................................................................................................................
H+ ions .............................................................................................................................................
(ii) Write the rate equation for the reaction. (1)
(iii) Use the results for Run 1 and your rate equation from
(b)(ii) to calculate the value for the rate constant, k. Include units in your answer. (3)
(c) The presence of bromate(V) ions in drinking water is harmful to humans.
Bromate(V) ions can be converted to less harmful bromide ions by passing the water through palladium with a reducing agent.
Describe how a heterogeneous catalyst, such as palladium, increases the rate of a reaction. (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(Total for question = 13 marks)
Q23. The mechanism for the rapid decomposition of hydrogen peroxide, H2O2, in the presence of iodide ions, is:
(a) Write the overall equation for the reaction and hence state the role of the iodide ions. (2) ............................................................................................................................................. .............................................................................................................................................
(b) In further experiments, a student calculated the rate constant for the decomposition of hydrogen peroxide at two different temperatures.
The rate constant (k) is related to the temperature, T, (in Kelvin) by the following equation:
Use the data in the table to calculate the activation energy, Ea, for the reaction by a non-graphical method.
Give your answer in kJ mol–1 and to an appropriate number of significant figures.
Include a sign in your answer. (4)
(c) If acid conditions are used, the decomposition of hydrogen peroxide proceeds by a different mechanism.
The equation for this reaction is:
This reaction is first order with respect to both iodide ions and hydrogen peroxide.
The progress of this reaction is usually followed by adding a fixed quantity of sodium thiosulfate solution and a little starch solution to the reaction mixture, then timing the appearance of a blue-black colour.
This is known as a clock reaction. (i) Explain the formation of the blue-black colour and why its appearance is delayed. (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(ii) Although the oxidation of thiosulfate ions (S2O3 2– ) by hydrogen peroxide is thermodynamically favourable, it does not take place in this clock reaction.
Suggest a reason for this. (1)
............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(Total for question = 10 marks)
If you need the markscheme, including the examiners' reports for each question, and more exam and teaching materials on this topic, contact me through the contact page