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In the iodine clock reaction, there are really two processes happening simultaneously. The first is a slow reaction producing iodine:
H2O2 (aq) + 2 I- (aq) I2 (s) + 2 OH- (aq)
However, the iodine is never seen because of the second very fast process in which it is immediately reduced back to colorless iodide ion:
I2 (s) + 2 S2O32- (aq) 2 I- (aq) + S4O62- (aq)
Thus, iodine is slowly formed and then instantly converted back to iodide ion until all the thiosulfate ion (S2O32-) is used up. At that point the iodine concentration shoots up and the intense blue color of the starch-iodine complex appears.
The time required to reach this point depends on the rates of the two reactions, and consequently on the concentrations of all the reactants.
Anything that accelerates the first reaction will shorten the time. This increasing the concentration of iodide, hydrogen peroxide, or acid (it neutralizes the hydroxide ion) will make T shorter.
On the other hand, increasing the thiosulfate concentration will have the opposite effect; it will take longer for the iodine color to appear.
Half life, t1/2, is the time it takes
for the [R] to decrease by 1/2.
This is exactly like radioactive decay.
KMnO and t4 + H2C2O4 (oxalic acid)Figure 14.11: Two test tubes containing the same solution,one in water. Photo courtesy of American Color.
KMnO and t4 + H2C2O4 (oxalic acid)
CO2+ H2OFigure 14.11: One test tube shows a reaction while theother does not. Photo courtesy of American Color.
or reaction.Collision Theory and the Arrhenius Equation
y = b + m x
andThe Arrhenius Equation