Experiment Kinetics:The lodine Clock Reaction Obiectives Introduction In virtually every facet of chemical research.the ability to discover the kinetics of the reaction being studied is the key to understanding the overall chemistry.In a kinetic study,one investigates the rates at which reactions occur and how those rates are affected by changes in the concen and the presence of catalysts.Once factors are In this experiment,the reaction between iodide,and peroxydisulfate,SOis studied 3I(aq)+S,O-(aq)I(aq)+2S,O-(aq) The reaction kinetics will be investigated by the method,that is,measuring the amount if time that it takes for a certain fixed amount of the reactants to react.By measuring the time interval under various conditions of concentration and temperature,the rate law can be determined. For in,the rate depends upo a number of factors,the most imporant being of the and the rate constant,The rate econstant,in turn,depends on the reaction under study,but for any given reaction,varies only with temperature The rate is calculated as a change in concentration over a time interval (At)and has the units mol Lsec During each of several runs under different conditions,we will determine the length of time(At)required for the concentration of one of the reactants (S)to change by a certain fixed amount ()This is similar to timing runers inrace.By measuring the amount of tom it takes each runne rto run 1000 meters,we can calculate their running rates [A(distance)/A(time)] units of meters sec Determining the Order of Reaction What va riables eed tobe considered?The kinetics of be using the general rate law Rate=k[[S,O where a andare termed the orders of reaction with respect to iodide and peroxydisulfate.The maters the reactionrinh ow oncnrio ioe compi ha ing five variables (the twe oncentrations, a,b,and the rate and a known concentration of peroxydisulfate (S).The change in the peroxydisulfate concentration with time(which is the rate)can be calculated from the elapsed time for the reaction.This eliminates two variables,leaving three unknowns in the rate equation(a,b and the PDF文件使用"pdfFactory Pro”试用版本创建ww,fineprint.com,cnExperiment Kinetics: The lodine Clock Reaction Objectives • To determine the kinetic parameters (rate, order, rate constant) of a reaction. • To examine the effect of a catalyst on the rate of reaction. Introduction In virtually every facet of chemical research, the ability to discover the kinetics of the reaction being studied is the key to understanding the overall chemistry. In a kinetic study, one investigates the rates at which reactions occur and how those rates are affected by changes in the temperature, pressure, concentration, and the presence of catalysts. Once these factors are understood, the conditions may be optimized to speed up or slow down a reaction as desired. In this experiment, the reaction between iodide, I- , and peroxydisulfate, 2 S O2 8 - is studied: - 2 - 2 2 8 3 2 4 3I (aq)+S O (aq) I (aq) 2S O (aq) - - + The reaction kinetics will be investigated by the method of initial rates, that is, measuring the amount if time that it takes for a certain fixed amount of the reactants to react. By measuring the time interval under various conditions of concentration and temperature, the rate law can be determined. For reactions occurring in solution, the rate depends upon a number of factors, the most important being the concentration of the reactants and the rate constant, k. The rate constant, in turn, depends on the reaction under study, but for any given reaction, varies only with temperature. The rate is calculated as a change in concentration over a time interval (Δ[ ]/ Δt) and has the units mol L-1 sec -1 . During each of several runs under different conditions, we will determine the length of time (Δt) required for the concentration of one of the reactants ( 2 S O2 8 - ) to change by a certain fixed amount (Δ[ ]). This is similar to timing runners in a race. By measuring the amount of tome it takes each runner to run 1000 meters, we can calculate their running rates [Δ(distance)/Δ(time)], units of meters sec -1 . Determining the Order of Reaction What variables need to be considered? The kinetics of this reaction can be approximated using the general rate law: -1 a 2 R 2 8 ate=k[I ] S O - é ù ë û where a and b are termed the orders of reaction with respect to iodide and peroxydisulfate. The above rate law is fairly complex, having five variables (the two concentrations, a, b, and the rate constant). To simplify matters, the reactions is run staring with a known concentration of iodide (I-) and a known concentration of peroxydisulfate ( 2 S O2 8 - é ù ë û ). The change in the peroxydisulfate concentration with time (which is the rate) can be calculated from the elapsed time for the reaction. This eliminates two variables, leaving three unknowns in the rate equation (a, b and the PDF 文件使用 "pdfFactory Pro" 试用版本创建 www.fineprint.com.cn