EXP.2 RESOURCE 2 - WARNING NOTICE The experiments described in these materials are potentially hazardous and require a high level of safety

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III. Chemical Kinetics III.1- The Iodine Clock Reaction Introduction In this experiment, you will study a reaction that proceeds at an easily measured rate at room temperature: S 2 O 8 2- + 2I - 2SO 4 2- + I 2 persulfate iodide sulfate iodine In the first part of the experiment, the rate equation will be determined by investigating the effect of the concentration of the reactants on the rate of the persulfate-iodide reaction. In the second part, the activation energy will be calculated by studying the effects of temperature change and addition of a catalyst on the reaction system. Background Given the equation for a general reaction: aA + bB ± ² Products ± The dependence of the rate of the reaction on the concentration of the reactants may be expressed by a rate equation of the form: rate = k [ A ] l [ B ] m where, k is the rate constant (or rate coefficient); l and m are the orders of the reaction with respect to the reactants A and B, respectively; and the sum l + m is the overall reaction order. Unlike the stoichiometric coefficients determined by calculation, the orders of the reaction are based on the kinetics of the reaction. The orders of the reaction are defined by the mechanism of the reaction , which is an account of the actual steps by which the molecules combine. Orders can only be determined experimentally. The effect of temperature on reaction rate is given by the Arrhenius equation: a k = A e - E / RT where A is the Arrhenius constant, E a the activation energy of the reaction, T the absolute temperature, and R the universal constant of gases. Description of the Experiment In this experiment, we study the kinetics of the reaction between persulfate S 2 O 8 2- and iodide I - ions: 29 WARNING NOTICE: The experiments described in these materials are potentially hazardous and require a high level of safety training, special facilities and equipment, and supervision by appropriate individuals. You bear the sole responsibility, liability, and risk for the implementation of such safety procedures and measures. MIT shall have no responsibility, liability, or risk for the content or implementation of any of the material presented. Legal Notice
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S 2 O 8 2 ± + 2I ± ²²²²³ 2SO 4 2 ± + I 2 (1) persulfate iodide sulfate iodine Rates of reaction are measured by either following the appearance of a product or the disappearance of a reactant. In this experiment, the rate of consumption of the iodine will be measured to determine the rate of the reaction. As reaction (1) runs, the amount of iodine (I 2 ) produced from it will be followed using reaction (2): 2S 2 O 3 2 ± + I 2 ²²²²³ S 4 O 6 2 ± + 2I ± (2) t hiosulfate iodine tetrathionate iodide The iodine produced from the persulfate-iodide reaction (1) is immediately reduced back to iodide by thiosulfate ions (2). A known amount of thiosulfate ions will be added to the reaction
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This note was uploaded on 11/13/2011 for the course CHEM 1b taught by Professor Cabrera during the Spring '10 term at San Jose City College.

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EXP.2 RESOURCE 2 - WARNING NOTICE The experiments described in these materials are potentially hazardous and require a high level of safety

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