kineticEXAMPLE2009 - Experiment 2 Chemical Kinetics a Clock...

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Experiment 2 – Chemical Kinetics, a Clock Reaction Chem 102 March 3, 2009 Abstract In this experiment, a set amount of sodium thiosulfate was used to interact with the I 2 product from the primary reaction. Thus, creating a clock reaction and paralleled the time it took for a color change with the time to produce a necessary amount of I 2 . By using different mixtures of reactants and measuring the time it would take for the solution to turn blue, which is a result of the I 2 interacting with the starch, the dependence of the reaction rate of concentration was demonstrated. With greater concentration of the reactants, I - , BrO 3 - , and H + , in the reaction, the time it took for the color change was faster. Along with concentration, the dependence of reaction rate on temperature was shown by a faster reaction time when the reaction was performed at 40C in comparison to 0C. The use of ammonium molybdate demonstrated the dependence of reaction rate on a catalyst by lowering the activation energy and speeding up the reaction eleven folds. Therefore, the three separate parts of this experiment validated how concentration, temperature, and a catalyst affect the reaction rate. The individual orders for I - , BrO 3 - , and H + are 1, 1, and 2 respectively. The overall order of the reaction is 4, the average rate constant is 2929 1/M 3 s, and the activation energy is 45.3 kJ/mol. Introduction Chemical kinetics encompasses the study of reaction rates, how these rates change due to conditions, and the molecular level activity that occurs in a reaction. The four common variables that influence reaction rate are the concentration of the reactant, temperature, catalyst, and surface area. For a reaction to occur, the molecules must collide and more collisions occur with increased thermal energy to greater number of molecules present. To further the understanding of chemical kinetics and the reaction rates dependence on concentration, temperature, and the presence of a catalyst, this experiment focused on the primary reaction between iodide, bromate, and hydrogen ions (1) and determining the reaction’s rate law (2): 6I - (aq) + BrO 3 - (aq) + 6H + (aq) 3I 2 (aq) + Br - (aq) + 3H 2 O(1) (1) rate = k[I - ] x [BrO 3 - ] y [H + ] z (2) In this reaction, there are three reactants and different concentrations of each reactant were used in the five different mixtures to obtain the orders, x, y and z. Hence, the rate constant k can then be calculated. It is expected that the reaction occurs more quickly in the presence of greater concentration of reactants.
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In order to make sure that the same small amount of I 2 product formed for each mixture reaction, sodium thiosulfate was used to create a clock reaction (3) that occurred faster than the
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kineticEXAMPLE2009 - Experiment 2 Chemical Kinetics a Clock...

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