NJC Physical Chemistry Revision – Kinetics

National Junior College 2016 H2 Chemistry Revision Package Physical Chemistry Revision – Kinetics MCQ 1 [CJC 2011] Two substances, A and B, react according to the following equation: A + 2 B → C To determine the order of reaction with respect to each substance, four experiments were performed and the results are shown below: Experiment [A] / mol dm-3 [B] / mol dm-3 Initial rate of formation of C / mol dm-3 min-1 1 0.10 0.10 0.0010 2 0.40 0.10 0.0160 3 0.10 0.20 0.0020 4 0.20 0.20 ? Which is the correct value for the initial rate of formation of C for experiment 4? A 0.0040 B 0.0080 C 0.0160 D 0.0320 2 [VJC 2009] An experiment was carried out to investigate the initial rate of reaction between ammonium peroxodisulfate, (NH 4)2S2O8, an oxidising agent, and potassium iodide, KI. The initial concentrations of (NH 4)2S2O8 and KI solutions in the mixture together with the time taken for the mixture to darken for the various experimental runs are given below. Initial [(NH4)2S2O8] /mol dm-3 Initial [KI] /mol dm-3 Time taken to darken /s 0.10 0.20 35 0.05 0.20 70 0.10 0.067 105 0.02 0.75 ? What is the expected time taken(in seconds) to darken when the experiment is repeated using initial concentrations of(NH4)2S2O8 and KI to be 0.02 mol dm-3 and 0.75 mol dm-3 respectively?

National Junior College 2016 H2 Chemistry Revision Package A 40 B 47 C 60 D 72 3 [VJC 2009] Which of the following statements best explains why a small increase in temperature leads to a significant increase in the rate of a gaseous reaction? A The frequency of collisions between the molecules is greater at a higher temperature. B The activation energy of the reaction is lower when the gases are at a higher temperature. C The average kinetic energy of the molecules is greater at a higher temperature. D The frequency of effective collisions between molecules with kinetic energy greater than the activation energy is greater at a higher temperature. 4 [HCI 2007] 5 The following data were obtained from the studies of the reaction between NO and O2 in a vessel at constant temperature. Which of the following statements are true regarding the above reaction? 1 The overall order of the reaction is 2. 2 The rate-determining step involves 1 oxygen molecule.

National Junior College 2016 H2 Chemistry Revision Package 3 The rate constant has units of atm−2s−1. A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only 6 [PJC 2011] The kinetics of the reaction between iodide and peroxodisulfate can be investigated by varying the volume of the reactants used. The two reactants are mixed in the presence of a known and small amount of Na2S2O3 and a little starch. S2O82-(aq) + 2I-(aq) → 2SO42-(aq) + I2(aq) The time taken for an intense blue colour to be observed is then determined. Experiment Volume used / cm3 Time / s 1.0 mol dm-3 KI 0.040 mol dm-3 Na2S2O8 H2O 1 10.0 5.0 25.0 170 2 15.0 5.0 20.0 113 3 15.0 10.0 15.0 56.5 4 20.0 X y 21.3 What are the values of x and y in Experiment 4? x y A 5.0 15.0 B 10.0 10.0 C 15.0 5.0 D 20.0 0.0

National Junior College 2016 H2 Chemistry Revision Package 7 [RI 2009] 8 [HCI 2009] The bromination of propanone is acid-catalysed. CH3COCH3 + Br2 ⎯⎯→⎯ +H CH3COCH2Br + H+ + Br ─ The rate of disappearance of the colour of bromine was measured for several different concentrations of propanone, bromine and H + at a certain temperature and the results tabulated below. Expt [CH3COCH3]/ mol dm─3 [Br2]/ mol dm─3 [H+] / mol dm─3 Rate of disappearance of Br2 colour / mol dm─3 s─1 1 0.30 0.05 0.05 5.70 x 10─5 2 0.30 0.10 0.05 5.70 x 10─5 3 0.30 0.05 0.10 1.14 x 10─4 4 0.40 0.05 0.20 3.04 x 10─4 Which of the following statements about the above reaction is true? A The rate equation for the reaction is rate = k[CH3COCH3][Br2]. B The rate constant for the reaction is 3.8 x 10─3 mol─1 dm3 s─1. C The rate constant of the reaction doubles when [CH3COCH3] is doubled. D The rate constant of the reaction remains unchanged when temperature is doubled.

National Junior College 2016 H2 Chemistry Revision Package 9 [ACJC 2011] An experiment was carried out to investigate the initial rate of reaction between ammonium peroxodisulfate, (NH4)2S2O8, an oxidising agent, and potassium iodide, KI. S2O82-(aq) + 2I-(aq) → 2SO42-(aq) + I2(aq) The initial concentrations of (NH4)2S2O8 and KI solutions in the mixture, together with the time taken for the mixture to darken for the various experimental runs are given below: Experiment Initial [(NH4)2S2O8] / mol dm-3 Initial [KI] / mol dm-3 Time taken to darken / s 1 0.10 0.20 35 2 0.05 0.20 70 3 0.10 0.067 105 4 0.02 0.75 ? Which of the following statements about the reaction is/are true? 1 The reaction involves the formation of an intermediate. 2 The time taken for the mixture to darken in Experiment 4 is 47 s. 3 The slow step involves the reaction between one S2O82− and one I−. A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only 10 [NYJC 2011] The kinetics of the reaction between iodide and peroxodisulfate can be investigated by varying the volume of the reactants used. The two reactants are mixed in the presence of a known amount of Na2S2O3 and a little starch. The time taken for an intense blue colour to be observed is then determined. Experiment Vol used / cm3 Time 1.0 mol dm-3 KI 0.040 mol dm-3 Na2S2O8 H2O(l) t / s 1 10.0 5.0 25.0 170 2 15.0 5.0 20.0 113 3 15.0 10.0 15.0 56.5 4 20.0 20.0 0.0 x What is the value of x in Experiment 4? A 11 B 21 C 85 D 1360

National Junior College 2016 H2 Chemistry Revision Package 11. [SAJC 2009] The table below gives data gathered from the reactions between Q and R at constant temperature. Experiment [Q] / mol dm -3 [R] / mol dm -3 initial rate / mol dm -3 s-1 1 0.3 0.2 4.0 × 10-4 2 0.6 0.4 1.6 × 10-3 3 0.6 0.8 6.4 × 10-3 What are the units of the rate constant for the reaction? A mol2 dm-6 s-1 B mol-2 dm6 s-1 C mol dm-3 s-1 D mol-1 dm3 s-1 12 [CJC 2011] A student proposed that the conversion of nitrogen monoxide, NO, to nitrogen dioxide is second-order with respect to nitrogen monoxide. Which graphs show that the student’s proposal may be correct? 1 2 3 A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only 13 The reaction between KI(aq) with excess Na2S2O8(aq) was studied and the following graph was obtained. Rate [NO]2 Rate [NO] Rate [NO] C∞ [I2]

National Junior College 2016 H2 Chemistry Revision Package Which of information may be obtained from the graph above? 1 the rate of reaction at any given instant 2 order of reaction with respect to I− 3 order of reaction with respect to S2O82− A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only 14 [AJC 2011] The rate of decomposition of aqueous H 2O2 increases in the presence of the enzyme, catalase. 2H2O2 2H2O + O2 The following graph was obtained in a study to investigate the effect of catalase on the rate of decomposition of H2O2. The steps predicted for this enzymatic decomposition of H2O2 are shown below. catalase + H2O2 catalase–H2O2 complex slow step Catalase–H2O2 complex H2O + O2 + catalase fast step Which statements about the enzymatic decomposition of H2O2 are correct? Volume of O2 produced per unit time / cm3 s-1 [H2O2] time

National Junior College 2016 H2 Chemistry Revision Package 1 At low [H2O2], the rate of decomposition increases with increasing amount of catalase used. 2 At low [H2O2], catalase lowers the activation energy of the decomposition by forming temporary bonds with H2O2 molecules. 3 At high [H 2O2], all the active sites of the catalase enzyme are saturated with H2O2 molecules. A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only 15 [PJC 2011] Quaternary ammonium ions can undergo Hofmann elimination i