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Unformatted text preview: Austin Peay State University Department of Chemistry Chem 1121 The Iodine Clock: A Study in Kinetics Revision F7 Page 1 of 9 Suggested reading: Chang text – pages 532 – 554 Cautions These solutions may be toxic, irritants and corrosive. Avoid skin contact from all chemicals and wash thoroughly if contact occurs. Purpose The purpose of this experiment is to measure the effect of reactant concentration upon the rate of the reaction between the peroxydisulfate ion (S 4 O 6 2- ) and iodide ion (I- ), to experimentally determine the order of the reaction with respect to the reactant concentration, and to obtain the rate law for the chemical reaction. Introduction This experiment will investigate a reaction occurring at different rates as a result of varying the concentration of reactants. Two examples illustrating the difference in the rate of reaction include the rusting of iron as a reasonably slow reaction while the decomposition of TNT is an extremely fast reaction. Kinetics is the area of chemistry that deals with the studying of the rates of reactions. Four main factors that control the rates of homogeneous reactions in solution include the nature of the reactants, the concentration of the reactants, the temperature of reaction, and the use of catalysts. Reactions will only occur when reactant molecules obtain enough energy to interact or collide with other reactant molecules. Each one of the factors above affects how reactant molecules interact or collide with each other. As the concentration of a solution changes, the number of particles per unit volume changes. This can be advantageous because an increase in the number of particles per unit volume will increase the probability of collisions between reacting species and therefore the rate of the reaction will increase. In a simplistic model, temperature can be used as a measure of the average kinetic energy of a reaction. As the temperature of a reaction increases, the kinetic energy of reacting species increases. As a consequence of increased kinetic energy, the number of collisions between reacting species is increased and the rate of reaction is increased. Catalysts are chemical species added to a reaction to increase the reaction rate. The mechanisms by which a catalyst increases the rate of reaction are numerous. An added catalyst can decrease the energy at which collisions occur, therefore allowing more collisions to occur and increasing the rate of reaction. A catalyst can also assist in the correct geometrical arrangement of reacting species necessary for collision thereby increasing the number of collisions and the rate of reaction. A major advantage of using a catalyst is that it remains chemically unchanged as a result of the reaction and can by recovered and/or reused. Catalysis is a branch of chemistry that is very vital in the production of many products used in our life such as plastics, petroleum, rubber and pharmaceutical products just to name a few....
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- Spring '07