### Introduction

A basic kinetic study of a chemical reaction often involves conducting the reaction at varying concentrations of reactants. In this way, you can determine the order of the reaction in each species, and determine a rate law expression. Once you select a reaction to examine, you must decide how to follow the reaction by measuring some parameter that changes regularly as time passes, such as temperature, pH, pressure, conductance, or absorbance of light.

In this experiment you will conduct the reaction between solutions of potassium iodide and iron (III) chloride. The reaction equation is shown below, in ionic form.

$2{\text{ }}{{\text{I}}^{{\text{ - }}}}{\text{(aq) + 2 F}}{{\text{e}}^{{\text{3 + }}}}{\text{(aq)}} \to {{\text{I}}_{\text{2}}}{\text{ (aq) + 2 F}}{{\text{e}}^{{\text{2 + }}}}{\text{(aq)}}$

As this reaction proceeds, it undergoes a color change that can be precisely measured by a Vernier Colorimeter or a Vernier Spectrometer. By carefully varying the concentrations of the reactants, you will determine the effect each reactant has on the rate of the reaction, and consequently the order of the reaction. From this information, you will write a rate law expression for the reaction.

### Objectives

In this experiment, you will

• Conduct the reaction of KI and FeCl3 using various concentrations of reactants.
• Determine the order of the reaction in KI and FeCl3.
• Determine the rate law expression for the reaction.