KINETICS CALCS AND GRAPHS INSTRUCTIONS

Transcription

1 KINETICS CALCS AND GRAPHS INSTRUCTIONS 1. Open a new Excel or Google Sheets document. I will be using Google Sheets for this tutorial, but Excel is nearly the same. 2. Enter headings across the top as shown below. You will be making graphs for [CV] vs time, ln[cv] vs. time and 1/[CV] vs. time. Note: I am just coloring the columns for my own benefit, you do not need to do the same. Be sure to include units wherever appropriate, as they will transfer onto your graphs later. 3. Start entering time intervals into column A: 0, 20, You can continue entering manually OR use a handy function of spreadsheets, pattern prediction. Select the three cells with time intervals: 5. Hover your cursor over the blue box at the bottom right corner until a cross-hatch (+) appears, then hold and drag down to cell 47. The cells should auto-populate with time intervals of 20 s to 900 s. 1

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3 6. While your time cells are still selected, copy and paste them to the other two Time columns. 3

4 7. Enter your absorbance values from your data table. This takes a bit of time, but make sure you are entering them correctly, as all your other calculations will be based off of them. You may have some empty cells at the beginning, as I have. That is ok, just leave them blank. 4

5 8. Time to look back in your lab packet for your trendline equation. Mine was: y = x When I substitute in A and c, it is A = c The next column I want to fill in is concentration, so rearranging this equation to solve for c, I get c = A/ This is the equation I want to enter into the spreadsheet. In the first concentration cell that has a corresponding absorbance, first type an equal sign. This signifies that you are entering an equation to be calculated. 9. Rather than typing the absorbance value, I am going to reference the cell with absorbance instead (you ll see why in a moment). Click on the absorbance cell next to the cell you are typing in or type the cell number (B4 in this case). 10. Now type the rest of your equation. 5

6 11. Press Enter to finish the calculation. 12. Now for the cool part (in my opinion!)...click on cell you just worked on and hover your mouse over the bottom right corner until a cross-hatch (+) appears. Hold and drag down through the rest of the cells in this column. Since you have a reference formula in the first cell, the spreadsheet assumes you always want to take the value from the cell to the left and divide it by (in my case). It will do all the calculations for you! 6

7 13. Now let s do the same for the natural log column. In the first ln[cv] cell that has a corresponding absorbance, first type an equal sign. Again, this signifies that you are entering an equation to be calculated. 14. Spreadsheets recognize many formulas. Type ln and it will recognize that you are doing a natural logarithm. 15. Open a parentheses, type the cell that contains [CV] for this row (NOT absorbance!), then close the parentheses. 7

8 16. Press Enter to calculate. 17. Once again, let s drag this formula to the rest of the ln[cv] cells and save ourselves a ton of manual calculations!! Click on cell you just worked on and hover your mouse over the bottom right corner until a cross-hatch (+) appears. Hold and drag down through the rest of the cells in this column. 8

9 18. Lastly, let s finish the inverse concentration column. In the first 1/[CV] cell that has a corresponding absorbance, first type an equal sign. Again, this signifies that you are entering an equation to be calculated. 19. Enter the formula, referencing the [CV] cell for this row (NOT absorbance!!). 20. Press Enter to calculate, then hold and drag the formula as you did before to the remaining cells. 9

10 21. Before going onto preparing the graphs, I am going to hide the Absorbance column. I will not be graphing any of these values and I don t want to accidentally include them. Right click on the column letter (B in my case), then select Hide Column. This doesn t delete the values, just obscures them from view temporarily. 22. Now my spreadsheet looks like this: If you want to see your absorbance values again, just click on the small arrows < > where column B used to be. 10

11 23. Time to graph. The first graph will be [CV] vs. time. If this is the most linear, the reaction is 0 order. Select the adjacent Time and [CV] columns (yellow highlight in my example). 24. With the columns selected, press the Chart icon. 11

12 25. The Chart Editor box will pop up. In the Chart types tab, scroll down and find the Scatter plot option. Notice in the preview that any titles, axes labels and units you previously types in the column headings transfer directly to your chart. Press Insert. 26. Your first chart is done! 12

13 27. Now select the adjacent Time and ln[cv] columns (red highlight in my example). If this graph is most linear, the reaction is 1st order. 13

14 28. With the columns highlighted, press the Chart icon again, select Scatter plot again in the Chart types menu and Insert the new chart. 29. The last graph will be the inverse concentration vs. time plot. If this graph is most linear, the reaction is 2nd order. Select the adjacent Time and 1/[CV] columns, then insert a new scatter plot chart, just as you did for the first two. 30. All done! If you are unsure which graph is most linear, add a trendline and R 2 value to each. The graph with an R 2 value closest to 1 is the most linear relationship. 14