Chemical Kinetic Lab Report

This assignment discusses chemical kinetics by determining the rate and average value for rate constant based on experimental values given. The orders of the reactants can only be determined experimentally, so we must look at how the concentration of the reactants affect the instantaneous initial rate while holding the concentration of the other reactant constant. In this reaction, the overall reaction order for the rate law is third because the order for A is second and the order for B is first. For A, when the concentration doubles in trial 3 compared to trial 1, the instantaneous initial rate quadruples, which indicates that it is second order. For B, when the concentration doubles in trial 2 compared to trial 1, the rate also doubles, indicating
first order. The rate law is rate = k[A]2[B], which we can use to find the average rate constant by solving for k for each trial and then averaging all the k's.
The rate constant for each trial is 0.103M-2s-1 so the average rate constant is 0.103 M-2s-1. The integrated rate law is an equation that links concentration of reactants with time, and the plot can show the order of the reactants. The integrated rate law plot that will yield a straight line for A is the plot of 1/[A] vs. time because A is a second order reactant. This is determined by the integration of the rate of disappearance of A: -d[A]/dt = k[A]2, which yields 1/[A]t = 1/[A]0 + kt. The slope of this graph will give the value of k, the rate constant of the reaction. The first order for B will show a straight line in the plot of ln[B] vs. time. This was found by integrating the rate of disappearance of B: -d[B]/dt = k[B], which results in ln[B]t = ln[B]0 - kt. The slope of this graph will give the value of -k, the rate constant of the reaction. Based on the balanced reaction, this reaction is not an elementary reaction. Because the rate reaction for an elementary reaction can derived from the balanced equation, the orders of reactants should be equal to the stoichiometric
coefficients. Since the orders of reactants do not equal to the coefficients of the balanced equation, this means that the rate law does not correspond to an elementary reaction. We found that the order of A is second and the order of B is first, which corresponds to the integrated rate law plot of 1/[A] vs time and ln[B] vs. time that yields a straight line. We also calculated the average rate constant to be 0.103 M-2s-1 and indicated that this is not an elementary reaction based on the rate law.