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. 

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