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		FAQ Index Question 1 My activation energy doesn't agree with my lab partner's. What could be wrong? Question 2 Why do I have to plot my data during the experiment? I hate that! Question 3 How do I extrapolate my data to find t = using the Least Squares Applet on the website? Submissions Submit a question or an answer to the FAQ Questions & Answers Question 1 My activation energy doesn't agree with my lab partner's. What could be wrong? Professor Milde Look carefully at the units for your calculation of the activation energy. You are plotting ln k vs. 1/T and the units of the slope will be units of temperature. To calculate the activation energy, you will multiply the slope times - R. So R should be in units of J/mol K, the temperatures and slope should be in units of K, giving an activation energy in J/mol units. Typical mistakes are to neglect to convert the temperature values to Kelvins and to use the gas constant R in the incorrect units. Question 2 Why do I have to plot my data during the experiment? I hate that! Professor Milde There are lots of good reasons to plot your data as you measure it. Plotting gives you a much better feel for trends in the data that may not be obvious if you just record the numbers. Looking at a plot may point out an experimental problem, like a mis-meaured reaction mixture or a drifting spectrometer, for example. It is better to find out about problems early in a run, rather than after spending 20 minutes recording data that is not useable! You can always use a graphing calculator to plot your data if paper and pencil seem too onerous. Question 3 How do I extrapolate my data to find t = using the Least Squares Applet on the website? Professor Milde You need the x intercept of your plot, or the time value when A = 0. The slope and intercept from the Least Squares applet give you the equation of the line. If you use this equation and substitute 0 for y, you can solve for the x value, which will be the x-intercept. Submissions Submit to the FAQ You can submit either a question or an answer to a question about this week's experiment. Your submission will be mailed to the site editor, who will respond to you directly and also add your submission to the FAQ page. Having trouble with the submission procedure? Check your Kerberos installation. If you lose the FAQ Submission window it may be hidden behind another browser window.
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