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Unformatted text preview: Section 5/Chemical Kinetics/ SKH Bishop Baker Secondary School AL Chemistry Section 5 Chemical Kinetics 80 IB Q.8 (a) The results of an experiment to investigate the rate of the reaction H 2 O 2 (aq) + 2 H + (aq) + 2 I- (aq) I 2 (s) + 2 H 2 O(l) at 298 K are given in the table below : (In the presence of I- (aq), I 2 (s) exist as I 3- (aq).) Run 1.0 M H 2 SO 4 0.1 M KI Water 0.1 M H 2 O 2 1/t cm 3 cm 3 cm 3 cm 3 s- 1 1 10.0 5.0 20.0 5.0 0.013 2 10.0 10.0 15.0 5.0 0.022 3 10.0 15.0 10.0 5.0 0.032 4 10.0 20.0 5.0 5.0 0.044 5 10.0 25.0 0.0 5.0 0.098 (i) Suggest a method for determining t for each sample, where t is the time for a small fixed quantity of I 2 to be formed. (3 marks) (ii) Using the given data, determine the order of this reaction with respect to iodide ion. (4 marks) (iii) How would you determine the order of this reaction with respect to H + (aq) ion ? (2 marks) (iv) If the reaction is found to be first order with respect to H 2 O 2 (aq) and zero order with respect to H + (aq) ion, what can you deduce about the rate determining step of this reaction. (1 mark) 81 IB Q.5 (a) The burning of magnesium ribbon is very vigorous and highly exothermic. (i) Draw a labelled energy profile for the reaction. (ii) Magnesium ribbon cannot be easily ignited by a burning match. Suggest an explanation for this. (2 marks) 82 IA Q.1 (a) Thiosulphate ions decompose in dilute hydrochloric acid according to the equation S 2 O 3 2- (aq) +2H + (aq) H 2 O(l) + SO 2 (g) + S(s) The kinetics of the above reaction can be studied by varying I. the thiosulphate ion concentration, II. the hydrogen ion concentration, and III. the temperature. (i) State what measurements or observations should be made in order to determine the initial rate in different runs of the reaction. (3 marks) 1 Section 5/Chemical Kinetics/ (ii) List the necessary chemical substances and apparatus required to carry out the above experiment. (4 marks) 82 IB Q.9 (b) What units are used for the following terms : (i) rate of reactions, and (ii) rate constant for first-order reactions ? (2 marks) (c) The radioactive isotope carbon-14 is formed by the bombardment of neutrons on nitrogen. Carbon-14, in turn, disintegrates by emitting -particles, the half-life of which is found to be 5570 years. (i) Write nuclear reactions in terms of atomic numbers and atomic mass numbers to how the formation of carbon-14 and its subsequent decay. (ii) If 32 counts per minute per gram of carbon is emitted by living organisms, while a fossilized bone gives 8 counts per minute per gram of carbon, calculate the age of the fossil. (5 marks) (d) The following endothermic reaction 2 A + B 2 2 AB proceeds in two steps as shown below : Step 1 A + B 2 intermediate (slow) Step 2 intermediate + A 2 AB (fast) (i) Sketch a diagram of enthalpy against reaction coordinate for the two-step reaction....
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- Fall '09