2. (2001) 3 I–(aq) + S2O82-(aq) I3–(aq) + 2 SO42-(aq) Iodide ion, I–(aq), reacts with peroxydisulfate ion, S2O82-(aq), according to the equation above. Assume that the reaction goes to completion. (a) In an experiment, equal volumes of 0.0120 I–(aq) and 0.0040 S2O82-(aq) are M M mixed at 25C. The concentration of I3–(aq) over the following 80 minutes is shown in the graph below. Indicate the time at which the reaction first reaches completion by marking an on the curve above at the point that corresponds to this time. Explain “X” your reasoning. (ii) Explain how to determine the instantaneous rate of formation of I3–(aq) at exactly 20 minutes. Draw on the graph above as part of your explanation. (b) Describe how to change the conditions of the experiment in part (a) to determine the order of the reaction with respect to I–(aq) and with respect to S2O82-(aq) . (c) State clearly how to use the information from the results of the experiments in part (b) to determine the value of the rate constant, for the reaction. k, (d) On the graph below (which shows the results of the initial experiment as a dashed curve), draw in a curve for the results you would predict if the initial experiment were to be carried out at 35C rather than at 25C. 3. 1997 B 2 A + B C + D The following results were obtained when the reaction represented above was studied at 25o C. Experiment Initial Initial Initial Rate of [A] [B] Formation of C (mol L-1 1 0.25 0.75 4.3x10-4 2 0.75 0.75 1.3x10-3 3 1.50 1.50 5.3x10-3 4 1.75 ? 8.0x10-3 (a) Determine the order of the reaction with respect to A and to B. Justify your answer.
2. (2001) 3 I–(aq) + S2O82-(aq) I3–(aq) + 2 SO42-(aq) Iodide ion, I–(aq), reacts with peroxydisulfate ion, S2O82-(aq), according to the equation above. Assume that the reaction goes to completion. (a) In an experiment, equal volumes of 0.0120 M I–(aq) and 0.0040 M S2O82-(aq) are mixed at 25C. The concentration of I3–(aq) over the following 80 minutes is shown in the graph below. Indicate the time at which the reaction first reaches completion by marking an “X” on the curve above at the point that corresponds to this time. Explain your reasoning. (ii) Explain how to determine the instantaneous rate of formation of I3–(aq) at exactly 20 minutes. Draw on the graph above as part of your explanation. (b) Describe how to change the conditions of the experiment in part (a) to determine the order of the reaction with respect to I–(aq) and with respect to S2O82-(aq) . (c) State clearly how to use the information from the results of the experiments in part (b) to determine the value of the rate constant, k, for the reaction. (d) On the graph below (which shows the results of the initial experiment as a dashed curve), draw in a curve for the results you would predict if the initial experiment were to be carried out at 35C rather than at 25C. 3. 1997 B 2 A + B C + D The following results were obtained when the reaction represented above was studied at 25o C. Experiment Initial [A] Initial [B] Initial Rate of Formation of C (mol L-1 1 0.25 0.75 4.3x10-4 2 0.75 0.75 1.3x10-3 3 1.50 1.50 5.3x10-3 4 1.75 ? 8.0x10-3 (a) Determine the order of the reaction with respect to A and to B. Justify your answer.