Continuing with your study of the degradation kinetics of Y in the presence of excess H+ so that [H+] >> [Y], you are interested in finding the activation energy, Ea,. Recall Y has a unique lmax at 254 nm, with a molar absorptivity ε of 4.55 x 103 cm-1 M-1 at 254 nm and the optical path length of b = 1.00 cm. The following data is collected from samples of Y with a starting (initial) concentration of 1.49 x 10-4 M:
Time
(hours)
Absorbance
(at λ = 254 nm)
Temperature (°C)
Time
(hours)
Absorbance
(at λ = 254 nm)
Temperature (°C)
1.0
0.668
16
1.0
0.669
18
2.0
0.664
16
2.0
0.662
18
3.0
0.660
16
3.0
0.654
18
4.0
0.656
16
4.0
0.647
18
5.0
0.652
16
5.0
0.640
18
6.0
0.648
16
6.0
0.633
18
7.0
0.643
16
7.0
0.626
18
8.0
0.639
16
8.0
0.619
18
9.0
0.635
16
9.0
0.612
18
10.0
0.630
16
10.0
0.605
18
11.0
0.626
16
11.0
0.598
18
12.0
0.622
16
12.0
0.592
18
13.0
0.618
16
13.0
0.586
18
14.0
0.614
16
15.0
0.610
16
1.0
0.669
19
16.0
0.606
16
2.0
0.659
19
17.0
0.602
16
3.0
0.649
19
18.0
0.598
16
4.0
0.639
19
19.0
0.594
16
5.0
0.630
19
6.0
0.621
19
1.0
0.665
17
7.0
0.612
19
2.0
0.659
17
8.0
0.603
19
3.0
0.653
17
9.0
0.594
19
4.0
0.647
17
10.0
0.586
19
5.0
0.642
17
11.0
0.577
19
6.0
0.636
17
12.0
0.568
19
7.0
0.631
17
8.0
0.625
17
1.0
0.664
20
9.0
0.620
17
2.0
0.652
20
10.0
0.614
17
3.0
0.639
20
11.0
0.609
17
4.0
0.627
20
12.0
0.604
17
5.0
0.615
20
13.0
0.599
17
6.0
0.603
20
14.0
0.594
17
7.0
0.591
20
15.0
0.589
17
8.0
0.581
20
16.0
0.584
17
9.0
0.569
20
10.0
0.559
20
1. Rate Constant kobs vs. Temperature T (12p). Build a summary table based only on the data from the previous page. In the table present the observed rate constant kobs values at the five different temperatures, T. Show all the graphical work, by pasting in all five EXCEL graphs (one for each temperature) below. Remember to properly title the plots, label the axes correctly and include the linear trend-line equations and R2 values. The summary table requires a title and properly labeled columns.
2. Activation Energy Ea (5p). Using EXCEL prepare an ln(kobs) vs. 1/T plot from the Question 1 kobs vs. T summary table that can be used to determine the activation energy Ea for the system. Paste-in this plot below and give the linear trend-line equation and R2 value (from EXCEL). State the Ea thus obtained. Show all work, explaining clearly how you derived the value of Ea from this plot.
3. Half-Life at 37.0 °C (5p). For the experimental conditions of the degradation study, calculate the t1/2 (half-life) for Y at 37.0 oC. Use equation (6) from the accompanying guide and the kobs at 23.5 oC from Lab Assignment 5. Show all work. Symbolically state the equations you are using. (Hint, the material in Unit 5 Module 3 under “Temperature Effects” may prove helpful.)
4. Percent of Drug Y Remaining (3p). For the experimental conditions of the degradation study, calculate the percent of drug Y remaining after 8.00 hours at 37.0 oC. Show all work. Symbolically state the equations you are using.
