1. Kinetics of the Iodine Clock Reaction Objective To fully determine the rate law for the iodine clock reaction using the method of initial rates

2. The Reaction The Rate Law x,y,z are the orders of reaction k is the rate constant A is the collision factor E a is the Activation energy

3. The Reaction The Rate These are colorless

4. How will we measure the Rate? We could monitor [I 2 ] t using UV/VIS spectroscopy But we will instead use the I 2 clock reaction and the method of initial rates

5. What is the I 2 Clock Reaction? To the reaction we add thiosulfate S 2 O 3 2- (aq) S 2 O 3 2- (aq) reacts very fast with any I 2 Only when all the S 2 O 3 2- (aq) is used up do we start to see I 2

6. Why do we add Starch? In addition to thiosulfate we will be adding a small amount of starch Starch is an indicator for I 2 In the presence of I 2 starch turns blue/black This will help us to see the I 2 when all the thiosulfate is used up

7. Measuring the Rate We have 3 reactions going on simultaneously As soon as all the S 2 O 3 2- is used up I 2 stays in solution and reacts with starch and the solution turns green/blue/black

8. Measuring the Rate We measure the time it takes for the solution to change color This is the time it takes all of the [S 2 O 3 2- ] o to get used up

9. Measuring the Rate Measure the time Δt it takes to turn blue then the rate is calculated as

10. Method of Initial Rates Make up flask 1 and flask 2 for a given mixture Pour flask 2 into flask 1 and start timing When solution starts to appear colored stop timer The time on the stop watch is Δt Write time on board Measure T( o C) Dispose down sink Repeat second trial