Abstract:

The goal of this experiment is to determine the rate of a reaction by way of kinetics. This is accomplished in a reaction between Crystal Violet and Sodium Hydroxide by measuring the concentration of the reaction over time, via a spectrophotometer. Then, by making use of the rate law, the concentrations of the chemicals in the reaction, and the change in time, we can calculate the rate. This equation is the rate law:

Then, as we are making use of absorbance, we must also make use of the Beer–Lambert law, to solve for the concentration:

A=εlc

(A=Absorbance, ε=the molar absorption coefficient, l=the path length through the solution that the light must travel, c=concentration)

Thus:

c=A/(εl)

Then, we must calculate the order of the reaction, as the equations used differ depending on the order of the reaction, as depicted in the table below:

Characteristics of Reaction Order:

One way to go about finding the order to which the reaction applies is to then measure the initial rate of reaction under varying concentrations of the reactants.

Which then becomes:

Then, if we set it so that the second experiment (differentiated with the subscript 2, as compared to experiment 1) uses double the initial concentration of one of the reactants (in this case OH-), we can simplify to the following equation, and solve for n:

Then, by repeating the process for the Crystal Violet in a third experiment, we can solve for m:

Finally, in knowing this, we can calculate the rate, and, then, with that, using the equation for the particular order, the rate constant.