Cyclohexene and bromine react to form 1,2-dibromocyclohexane as shown in the equation below:
C6H10+Br2→C6H10Br2\text{C}_6\text{H}_{10} + \text{Br}_2 \rightarrow \text{C}_6\text{H}_{10}\text{Br}_2C6H10+Br2→C6H10Br2
A student investigates the kinetics of this reaction by monitoring the concentration of bromine over time. The initial concentrations of the reactants are given in the table below:
\begin{tabular}{|l|c|} \hline & Concentration / \textbf{Concentration / }Concentration / mol dm−3\text{mol dm}^{-3}mol dm−3 \ \hline Br2\text{Br}_2Br2 & 0.0200 \ \hline C6H10\text{C}_6\text{H}_{10}C6H10 & 2.0000 \ \hline \end{tabular}
In this investigation, the concentration of cyclohexene is in large excess and the order with respect to cyclohexene can be assumed to be zero. The student records the concentration of bromine at various times to plot the concentration-time graph below:
Data Table: \begin{tabular}{|c|c|} \hline Time / s\textbf{Time / s}Time / s & [Br2] / mol dm−3\textbf{[Br}_2\textbf{] / mol dm}^{-3}[Br2] / mol dm−3 \ \hline 0 & 0.0200 \ 400 & 0.0141 \ 800 & 0.0100 \ 1200 & 0.0071 \ 1600 & 0.0050 \ 2000 & 0.0035 \ 2400 & 0.0025 \ \hline \end{tabular}
Why can the order with respect to cyclohexene be assumed to be zero in this investigation?
Show that the reaction is first order with respect to bromine. Determine the initial rate of reaction and the rate constant, kkk, including units.
Write chemical equations to suggest a two-step mechanism for the reaction, given further experiments show that the reaction is first order with respect to both cyclohexene and bromine.
Suggest how the investigation could be modified to show that the reaction is first order with respect to cyclohexene.