Question
2. Vant Hoff Analysis. In Problem 1 above, you obtained K C at a specific temperature for BDa . In a similar manner K C
2. Vant Hoff Analysis. In Problem 1 above, you obtained KC at a specific temperature for BDa. In a similar manner KC can be determined for BDa and BDb over a range of discrete temperatures. Assume, after some effort, you obtain the following KC vs. T results for molecular dyes BDa and BDb:
KC at Various Temperatures T for BDa |
| KC at Various Temperatures Tfor BDb | ||
T ( C) | KC |
| T ( C) | KC |
3.8 | 2.18 |
| 1.5 | 2.26 |
6.7 | 1.89 |
| 3.4 | 0.974 |
9.7 | 1.61 |
| 5.4 | 0.454 |
12.9 | 1.36 |
| 7.7 | 0.185 |
16.5 | 1.14 |
| 10.1 | 0.0747 |
20.1 | 0.957 |
| 12.1 | 0.0347 |
23.8 | 0.814 |
| 13.9 | 0.0168 |
Using EXCEL determine DH and DS for eachdye. Paste-in the plots below with the linear trend-line equation and R2 adjusted for reasonable sig figs. Remember, in this course all graphs must be appropriately scaled, titled and labeled. Please remember to do this without further reminders. Include all calculations, that is, show all work to clearly indicate how you determined the enthalpy and entropy values for BDa and BDb. (Remember to firstsymbolically state the equations).
3. Gibbs Free Energy. Given the DH and DS results above, calculate DG at 1.0 C for both dyes. Repeat the calculations for bothdyes, but at 5.0 C. Show all work. It is highly recommended to carry out the sub-calculations with 4 - 5 significant figures, and only round to the correct SF at the end this avoids rounding errors. Assume DH and DS remain constant over the 1 - 5 C range.
4. Analysis I. Given the results above, what do the calculated DG results indicate about the directionality (product vs. reactant) of each system (BDa and BDb) at 5.0 C versus 1.0 C?
BDa:
1 C: Since delta G is < 0, the product is favored. With delta H < 0 the product is energetically favored. It is entropically disfavored since delta S < 0.
5 C: Since delta G is < 0, the product is favored. With delta H < 0 the product is energetically favored. It is entropically disfavored since delta S < 0.
If the product is favored, the reactant is disfavored meaning the more intense the chromic shift will be.
BDb:
1 C: Since delta G is < 0, the product is favored. With delta H < 0 the product is energetically favored. It is entropically disfavored since delta S < 0.
5 C: Delta G of the reactant not the product is favored since delta G is > 0. With delta H < 0 the product is energetically favored. It is entropically disfavored since delta S < 0.
If the reactant is favored, the product will be disfavored. The chromatic shift will be less noticeable.
5. Analysis II. As you know, certain raw vegetables when subjected to freezing temperatures loose desirable qualities such as flavor and firmness. Suppose you are tasked with designing an inexpensive thermochromic thermometer that can be attached to vegetable shipping pallets and indicate if freezing temperatures exist. In this application the thermometer must sharply undergo a chromic shift (give a rapid, distinct color change) around 2 - 4 C. Given the results from Questions 2 - 4 above, and assuming the and maxvalues of both dyes are essentially identical, which dye, BDa or BDb, would be the best choice for such a thermochromic thermometer? Clearly justify your claim using the relevant data. To receive credit, you must respond with well written, very legible, complete sentences that correctly employs chemical terminology and concepts.
I need help with #5 please. I am not sure how to interpret the data.
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