ChemLab - Chemistry 6 - Week 2

Week 2: Chemical Kinetics 2

Overview

Getting Started

Techniques

Procedure

FAQ

Full Lab Manual

Introduction & Goals

Chemistry & Background

Key Questions

Prelab Problems

Safety

Procedure

In Your Write-up

Experiments Index

ChemLab Home

Before Lab
Make sure that your prelab is complete before coming to lab. Discuss your procedure with your lab partner before writing your prelab procedure and analysis flowchart or sample calculations. Be sure to complete the three prelab problems in the manual this week.

In Lab
For all the experiments this week, it is important that your written procedure detail clearly what was done in the lab. Use tables to summarize experimental conditions, where appropriate. Describe how the concentration conditions were arrived at so that each run was completed in a reasonable time period. All data must be plotted to check for linearity before you leave the lab. Plan to plot an Arrhenius plot of your temperature data, to check for linearity, also. Remember to record the name of your lab partner and to reference your partner's lab notebook if you need to transcribe original data from it into your notebook.

After Lab
Your notebook should include the following in the Results section:

• Plots analogous to Figure 1 for each kinetic run from last week and this week. Several plots can be presented on a single graph. From the slope of each plot, the value of the rate, -d([I₂]+[I₃^-])/dt for that run should be calculated. If the Least Squares program is used to determine the slope of your lines, your write-up can include either hand-plotted and computer graphs.

• Calculation of the rate constant k for each of last week's and this week's runs, and comment on the degree of constancy of k for last week's runs at one temperature.

• Use a statistical analysis to calculate the uncertainty in your average value of k at last week's temperature. This uncertainty analysis should include the following calculations and results. See the section on error and uncertainty in the beginning of this manual for details.

	- A mean value of k, from averaging all of last week's runs at one temperature
	- The standard deviation of that mean value of k from last week.
	- A 95% confidence interval of the mean for last week's rate constant, using the standard error and the student's T statistic.

For the temperature dependence experiment your results should include

• Plots and calculated k values for a minimum of four different temperatures, including last week's room temperature value.

• An Arrhenius plot and calculation of the activation energy of the reaction. Use a linear regression or least squares analysis to determine the slope of your Arrhenius plot and calculate the activation energy from this slope. Report the 95% confidence interval in the slope given by the Least Squares Program. Use error propagation to calculate the uncertainty in the activation energy from this uncertainty in the slope.