Determination of the Rate Equation for the Reaction between Hydrogen Peroxide and Iodide Ions
Reaction:
2I− + H2O2 + 2H+ → I2 + 2H2O
Objective:
To determine the rate equation and order of the reaction with respect to each reactant.
Experimental Procedure:
Data:
Experiment | [I-] (mol/L) | [H2O2] (mol/L) | Initial Rate (mol/L·s) |
---|---|---|---|
1 | 0.10 | 0.10 | 1.2 × 10^-5 |
2 | 0.20 | 0.10 | 2.4 × 10^-5 |
3 | 0.10 | 0.20 | 2.4 × 10^-5 |
Analysis:
Determine the order with respect to iodide ions [I−]:
Compare Experiments 1 and 2, where the concentration of [I−] is doubled while [H2O2] is kept constant. The initial rate also doubles, indicating that the reaction is first order with respect to iodide ions.
Order with respect to [I−]=1
Determine the order with respect to hydrogen peroxide [H2O2]:
Compare Experiments 1 and 3, where the concentration of [H2O2] is doubled while [I−] is kept constant. The initial rate also doubles, indicating that the reaction is first order with respect to hydrogen peroxide.
Order with respect to [H2O2]=1
Overall Reaction Order:
The overall order of the reaction is the sum of the individual orders:
Overall order=1 (order with respect to [I−]) + 1 (order with respect to [H2O2]) = 2
Rate Equation:
Based on the orders determined, the rate equation for the reaction can be written as:
Rate = k [I−] [H2O2]
where k is the rate constant.
Conclusion:
The reaction between hydrogen peroxide and iodide ions is second order, with first-order dependence on both iodide ions and hydrogen peroxide.
This example demonstrates how initial rate analysis can be used to determine the rate equation and order of a reaction. The same approach can be applied to other reactions with different reactants and conditions.