Iodine-Clock Reaction

Topics: Chemical reaction, Chemical kinetics, Reaction rate Pages: 9 (2660 words) Published: January 15, 2013

Chemical kinetics involving reaction rates and mechanisms is an essential part of our daily life in the modern world. It helps us understand whether particular reactions are favorable and how to save time or prolong time during each reaction. Experiment demonstrated the how concentration, temperature and presence of a catalyst can change the rate of a reaction. 5 runs of dilution and reaction were made to show the effect of concentration on chemical reactions. A certain run from the previous task was twice duplicated to for a “hot and cold” test for reaction rate. The prior run was again duplicated for a test with catalyst. The data obtained was graphed in a linear regression form, using the Arrhenius equation: lnk=-EaR-1T+lnA, reaction rate: rate = k[A]x[B]y and other principles held in chemistry. The graph from the results determined that there is a relation between rate and the previously mentioned factors. The results validated the notion that temperature, concentration and catalysts can manipulate chemical kinetics.


Chemical kinetics is an essential part of our lives. It determines the rates of reactions and how quickly reactants are converted to products. These reaction rates tell us how much time it would take to wait for a change, a physical change [1]. Chemical kinetics can be altered and controlled by five different factors, namely: the temperature at which the reaction occurs, application of pressure, concentration of reactants, nature of reactants and the presence of a catalyst. In this experiment, three of these factors are used to determine and validate their effects to the reaction rate, these factors are the temperature, the catalyst and the concentration of the reactants. S2O82- + 2I-  2SO42- + I2 (1)

The rates of a reaction (2) is defined by the rate law (3), where k is the rate constant, [A] is the concentration of reactant A, [B] is the concentration of reactant B and the powers x and y which gives the order of the reactions of A and B respectively, these values could be computed through the use of initial rates of a reaction. Substituting values from the rate law equation will give us the rate of product formation or decrease in concentration of the reactants in the persulfate-iodide reaction (4). This equation showed how the concentration of reactants modifies the rate of reaction. A + B  C + D (2)

Rate =k[A]x[B]y (3)
Rate = k[S2O82-]x[I-]y (4)
Regarding the effect of temperature on a reaction, we used the Arrhenius equation (5), this where Svante Arrhenius developed the mathematical relationship among activation energy, Ea, absolute temperature and the specific rate constant of a reaction, k, at a certain temperature. In this equation, A is a constant having the same units of k constant and T is the particular temperature as the reaction occurs. It is proportional to the frequency of collisions between reacting molecules that makes up a reaction. R is the universal gas constant expressed with the same units of energy with the activation energy.

k = A-Ea/RT (5)
Beaker A| Beaker B (+ 8 drops of fresh starch)|
Run| 0.2 M KI, mL| 0.2 M KCl, mL| 0.1 M K2S2O8| 0.1 K2SO4| 4mM Na2S2O3| 1| 10| 0| 5| 5| 5|
2| 5| 5| 5| 5| 5|
3| 2.5| 7.5| 5| 5| 5|
4| 5| 5| 7.5| 2.5| 5|
5| 5| 5| 10| 0| 5|
In the experiment, 5 different solutions are prepared for their reaction rates and each solution will be called a “run.” The 5 runs will be used to determine the effects of concentration on the reaction. The end of reaction will be determined as I2 reacts with the introduced starch solution, forming a blue solution. Conversely, this reaction is too slow and it needs sodium thiosulfate (Na2S2O3-2) to reduce iodine to iodide before the iodine reaction to starch can take place. Sodium thiosulfate was maintained at a...
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