The Kinetics of the Harcourt-Essen Reaction
The kinetics of the Harcourt-Essen Reaction (Hydrogen peroxide variation)
Aims:
To find the order of the reaction with respect to the Hydrogen Peroxide (H2O2), Potassium Iodide (KI) and the Sulphuric Acid (H2SO4) by the use of an Iodine clock reaction.
Calculate the rate constant, mechanism and equation
Find the effects of temperature on the rate of reaction
The effects of a catalyst on the rate of reaction
Find the activation enthalpy (Ea) of the reaction, with and without a catalyst
Background:
Hydrogen Peroxide and Potassium Iodide equation:
H2O2 + 2I - + 2H + I2 + 2H2O
No spectator ions
Iodine clock reactions
The Harcourt-Essen reaction has varying rates according to the concentration of Hydrogen Peroxide (H2O2) in the solution. The basic reaction involves the Hydrogen Peroxide, Hydrogen from the acid (H2SO4) and the Iodine ion from Potassium Iodide (KI):
H2O2 + 2I - + 2H + I2 + 2H2O
If the reaction doesn’t contain Sodium Thiosulphate (Na2S2O3) then the reactants would gradually go from clear to a yellow/brown colour when the iodine appears, this would make the reaction hard to time accurately.
When Sodium Thiosulphate is present it means there is a second very fast reaction between the iodine formed and the Thiosulphate ion:
I2 + 2S2O3 2- 2I - + S4O6 2-
The S2O3 2- ions consume the I2 instantaneous meaning that no brown iodine colour is produced until all the S2O3 2- ions
H2O2, KI are used up. Due to the iodine clock reaction consisting of only colourless solutions it is very hard to see when the reaction produces the yellow iodine. To aid with the iodine identification 1 cm3 of starch is added to the solution. Starch is added because when it is in the presence of iodine it will form a blue/black complex with the I2. It instantly turns blue/black once the S2O3 2- is used up giving a far more accurate time for the production of iodine ions and helps
Aims:
To find the order of the reaction with respect to the Hydrogen Peroxide (H2O2), Potassium Iodide (KI) and the Sulphuric Acid (H2SO4) by the use of an Iodine clock reaction.
Calculate the rate constant, mechanism and equation
Find the effects of temperature on the rate of reaction
The effects of a catalyst on the rate of reaction
Find the activation enthalpy (Ea) of the reaction, with and without a catalyst
Background:
Hydrogen Peroxide and Potassium Iodide equation:
H2O2 + 2I - + 2H + I2 + 2H2O
No spectator ions
Iodine clock reactions
The Harcourt-Essen reaction has varying rates according to the concentration of Hydrogen Peroxide (H2O2) in the solution. The basic reaction involves the Hydrogen Peroxide, Hydrogen from the acid (H2SO4) and the Iodine ion from Potassium Iodide (KI):
H2O2 + 2I - + 2H + I2 + 2H2O
If the reaction doesn’t contain Sodium Thiosulphate (Na2S2O3) then the reactants would gradually go from clear to a yellow/brown colour when the iodine appears, this would make the reaction hard to time accurately.
When Sodium Thiosulphate is present it means there is a second very fast reaction between the iodine formed and the Thiosulphate ion:
I2 + 2S2O3 2- 2I - + S4O6 2-
The S2O3 2- ions consume the I2 instantaneous meaning that no brown iodine colour is produced until all the S2O3 2- ions
H2O2, KI are used up. Due to the iodine clock reaction consisting of only colourless solutions it is very hard to see when the reaction produces the yellow iodine. To aid with the iodine identification 1 cm3 of starch is added to the solution. Starch is added because when it is in the presence of iodine it will form a blue/black complex with the I2. It instantly turns blue/black once the S2O3 2- is used up giving a far more accurate time for the production of iodine ions and helps