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Doha

A-Level Chemistry

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Published in: Chemistry
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A-level chemistry assignment answered Rates of Reaction. Study support. Model Answers.

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  1. QI. Solutions of two compounds, W and X, react together in the presence of a soluble catalyst, Y, as shown in the equation When the concentrations of W, X and Y are all doubled, the rate of reaction increases by a factor off r. Which is a possible rate equation for this reaction? A B C D rate — rate — rate = k [X] [Y] rate — A rate investigation was carried out on a reaction involving three reactants, X, Y and Z. The concentrations of the reactants were varied and the relative rate for each mixture determined. Experiment 3 [X]/mol dm-3 [Y]/mol dm-3 I x 10-3 2 x 10-3 1 x 10-3 2 x 10-3 2 x 10-3 [Z]/mol dm 2 x 10-3 2 x 10-3 4 x 10-3 xl.s Relative rate 4 0.5 The reaction is zero order with respect to Y. What is the overall order of reaction? c D 2 3 (Total 1 mark) (Total 1 mark)
  2. Q3. A series of experiments was carried out to find the order of reaction with respect to reactant X. In these experiments, only the concentration of X was changed. Which graph would show that the reaction is second-order with respect to X? rate of reaction concentration of X (Total 1 mark) Q4. The rate equation for the hydrogenation of ethene c2Ha(g) + H2(g) C2H6(g) is Rate = At a fixed temperature, the reaction mixture is compressed to triple the original pressure. What is the factor by which the rate of reaction changes? A B c D Q5. 6 9 12 27 (Total 1 mark)
  3. This question is about the reaction between propanonø and an excess of ethane-I ,2-diol, the equation for which is given below. CH3COCH3+ HOCH2CH20H (CH3)2 O—CH2 In a typical procedure, a mixture of 1.00 g of propanone, 5.00 g of ethane-I ,2-diol and 0.100 g of benzenesulphonic acid, C6H5S03H, is heated under reflux in an inert solvent. Benzenesulphonic acid is a strong acid. When the concentration of benzenesulphonic acid is doubled, the rate of the reaction It can be deduced that A B C D Q6. the reaction is first order overall. the reaction is third order overall. the reaction is acid-catalysed. units for the rate constant, k, are mol-2 dm6 s-1. Rate = k [AE [B] Correct units for the rate constant in the rate equation above are A B C D mol dm-3 s-1 mol-' dm-Ss m012 dm-6 s-1 mol-2 dm6 s-1 (Total 1 mark) mol- S- (Total 1 mark)
  4. Q7. The equation and rate law for the reaction of substance P with substance Q are given below. rate = Under which one of the following conditions, all at the same temperature, would the rate of reaction be slowest? [P] I mol dm 0.1 10 pH 2 4 (Total 1 mark) Q8. The rate equation for the acid-catalysed reaction between iodine and propanone is: rate = k [H*] [C3H60] The rate of reaction was measured for a mixture of iodine, propanone and sulfuric acid at pH = 0.70 In a second mixture the concentration of the sulfuric acid was different but the concentrations of iodine and propanone were unchanged. The new rate of reaction was a quarter of the original rate. What was the pH of the second mixture? 70 A B c D 1.00 1 .30 1.40 2.80 COL (Total 1 mark) X 0 -13 o. OAS
  5. Q9. Butadiene dimerises according to the equation 2?'?6 ??? 12 The kinetics of the dimerisation are studied and the graph of the concentration of ? sample of butadiene is plotted against time. The graph is shown below. 0.020 _01? 0,01 0,014 0_012 [Buta6iene] -3 0.010 ??1 dm ?.??? 0_006 0.004 0,002 ?_??? 'iiii"' 1000 2000 3000 4000 5000 7000 ???? s (?) Draw ? tangent to the curve when the concentration of butadiene is 0.0120 ??: dm-3. ? initial rat Use this value the reaction i reaction in this experiment has the value 4.57 ? 10-6 ??] dm-3 s-' „ ether with ? rate obtained from ???? tangent, to justify that the order of h respect to butadiene. ?.??\? -;tqso 0-0 ?. ? ??? S evor•X
  6. QIO. (a) (b) (5) (Total 6 marks) The following data were obtained in a series of experiments on the rate of the reaction between compounds A and B at a constant temperature. Experiment 2 3 Initial concentration Initial concentration of AJmol dm-3 o. 15 0.30 x L 0.60 of B/mol dm-3 0.24 0.24 048 Initial rate/mol dm-s s-1 0.45 x 10-s 0.90 x 10-5 7.20 x Show how the data in the table c be u with respect to A o däuce at the reaction is first-order (ii) 1 il D,Jd• Deduce the order with respect to B. g - IS WI, 2 fxpf.(imøvt The following data were obtained in a second series of experiments on the rate of the reaction between compounds C and D at a constant temperature. Experiment 4 5 Initial concentration Initial concentration of AJmol dm-3 0.75 0.20 of B/mol dm-3 1.50 o. 10 Initial rate/mol dm-3 s-1 9.30 x 10-5 To be calculated The rate equation for this reaction is rate = Use the data from Experiment 4 to calculate a value for the rate constant, k, at this temperature. State the units of k. Value for k Units of k -s q. 10
  7. (ii) QII. Calculate the value of the initial rate in Experiment 5. 0.10 0.10 ) (Total 6 marks) Gases A and B react as shown in the following equation. 2A(g) + B(g) The initial rate of the reaction was measured in a series of experiments at a constant temperature. The following rate equation was determined. rate = An incomplete table of data for the reaction between A and B is shown in the table. Experiment Initial [A] I mol 4.2 x 10-3 7.9 10-3 Initial [B] I mol 2.8 x 10-3 2.8 x 10-3 5.6 x 10 X Initial rate I mol 3.3 x -3 1.8 x 10-' 2 3 (a) (b) (c) Use the data from Experiment 1 to calculate a value for the rate constant, k, at this temperature. Deduce the units of k. Calculation -s Units mol clm S - Use your value of k from (a) to complete the table for the reaction between A and B. (If you have been unable to calculate an answer for (a), you may 2.3. This is not the correct answer.) (2) The reaction is zero order with respect to B.
  8. State the significance of this zero order for the mechanism of the reaction. (Total 6 marks) Q12. Kinetic studies enable chemists to suggest mechanisms for reactions. 2--q (a) (b) The following data were obtained in a series of experiments on the rate of the reaction between compounds A and B at a constant temperature. Experiment Initial concentration Initial concentration 2 3 of Almol dm-3 0.12 0.36 0.72 of Bimol dm-3 0.15 0.15 0.30 Initial rate/ mol dm-3 s-l 0.32 x 10-3 2.88 x 10-3 11.52 x IF (ii ) Deduce the order of reaction with respect to A Sec o Nk Deduce the order of reaction with respect to B (2) The following data were obtained in a series of experiments on the rate of the reaction between NO and 02 at a constant temperature. Experiment 4 5 Initial concentration of NO/mol dm-3 5.0 x 10-2 6.5 x 10-2 Initial concentration of 021mol dm-3 2.0 x 104 3.4 x 10-2 Initial rate/ mol dm-3 s-1 6.5 x 10-4 To be calculated The rate equation for this reaction is rate = Use the data from Experiment 4 to calculate a value for the rate constant, k, at this temperature, and state its units. 4 sr(0 Value of k - mol S
  9. (ii) (ii i) Q13. Units of k m O Calculate a value for the initial rate in Experiment 5. Using the rate equation, a scientist suggested a mechanism for the reaction which consisted of the two steps shown below. stepl NO + NO N202 Step2 N202+02-. Which did the scientist suggest was the rate—determining step? (5) (Total 7 marks) The initial rate of the reaction between gases D and E was measured in a series of experiments at a constant temperature. The results are shown in the table. Initial [D] I mol dm- Initial [E] I mol dm- Initial rate I mol dm-3 2 (a) (b) 1.25 x IF X S 188 x 10-2 1.88 x 10-2 5.81 x 1()-' 8.73 x 1 .75 1.16 x 3.92 x IF 1.57 x 10-1 Deduce the order of reaction with respect to D and the order with respect to E. Order with respect to D Order with respect to E Space for working Suggest why initial rates of reaction are us dt%determine ese rde ratherth rates!l_ of reaction at other times during the experiments.
  10. (c) Q14. State how the initial rate is obtained from a graph of the concentration of the product against time. ou wovu-ek (Total 5 marks) The Arrhenius equation can be written as: In k = The table below shows the value of the rate constant at different temperatures for a reaction. Rate constant Ids-I 6.13 x 10-5 2.75 x IF 8.25 x IF 8.23 x 10-3 In k Temperature/K Olly 700 727 746 793 Complete the table by calculating the values of In k and T at each temperature. Plot a graph of In k against T on the grid opposite. Use your graph to calculate a value for the activation energy, in kJ mol-I, for this reaction. To gain full marks you must show all your working. The gas constant R = 8.31 J K-1 mol-I
  11. (snaeul 8 ?-??? ?? 01 aWTb'l- (???- 011 • ? ?_??? ???

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