Chemical Kinetics, described as the study of rate of chemical processes, varies on many factors to determine the time needed for a reaction to complete. The rate of reaction of a chemical reaction is important, as reactions are of little use if the time period needed for the reaction to occur is too lengthy. Many factors influence the rate of a chemical reaction, such as temperature, concentration and surface area. The order of the reaction is based on the concentration of the reactants, and is what this lab focuses on.
To calculate the rate of a reaction, the individual concentration of the reactant species must be written out in an equation, and must be raised to a power, from which the order of the reaction can be obtained. The equation
Rate= k [A]n [B]m
gives the rate of the chemical equation. The proportionality constant, k, is called the rate constant, and quantifies the rate of a chemical reaction. An alternate way to determine the rate of a chemical equation is using the slope of a graph. If a concentration vs. time graph is plotted, the instantaneous rate of change represents the approximate rate. The instantaneous rate of the line is determined by finding the slope of the tangent at any time.
The order of a reaction is defined as the exponent to which the concentration term in the rate equation is raised, and is found through experimental trials. The total order of a reaction is determined by finding the sum of the individual orders of the reaction. The order of a reaction can be found using several methods, one being the measurement of the appearance over time of a coloured species. The progressing appearance of the coloured species is plotted as a function of time.
The partial order, with respect to the Cr(III) ion, can be found using the results obtained from the experiment conducted at the pH level of 4.0, 4.5, and 5.0. The rate expression for the reaction can be expressed in different forms, as
Rate= - ( (d[Cr(III)] ) / dt )