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
Ea is the Activation energy

3. The Reaction
The Rate
These are colorless

4. How will we measure the Rate?
We could monitor [I2]t using UV/VIS spectroscopy
But we will instead use the I2 clock reaction and the method of initial rates

5. What is the I2 Clock Reaction?
To the reaction we add thiosulfate S2O32-(aq)
S2O32-(aq) reacts very fast with any I2
Only when all the S2O32-(aq) is used up do we start to see I2

6. Why do we add Starch?
In addition to thiosulfate we will be adding a small amount of starch
Starch is an indicator for I2
In the presence of I2 starch turns blue/black
This will help us to see the I2 when all the thiosulfate is used up

7. Measuring the Rate We have 3 reactions going on simultaneously
As soon as all the S2O32- is used up I2 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 [S2O32-]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(oC)
Dispose down sink
Repeat second trial

11. Day 2: Getting Ea and A 2 measurements above RT
2 measurements below RT
2 measurements at RT
Write T(oC) and Δt on board
Use class data
ignition tubes
hotplate
reaction vessel 2
reaction vessel 1
thermometer
Allow the contents of vessel 1 and vessel 2 to reach thermal equiibrium with the water
Add the contents of vessel 2 into vessel 1 – and leave it in the beaker
Stir with the thermometer