WA 09_CHE-122-jan18 Sterile

Written Assignment 9: Spontaneity Reactions Answer all assigned questions and problems, and show all work. 1. How does the entropy of a system change for each of the following processes? (14 points) a. A solid melts. - increases b. A liquid freezes. - decreases c. A liquid boils. - increases d. A vapor is converted to a solid. - decreases e. A vapor condenses to a liquid. - decreases f. A solid sublimes. - increases g. Urea dissolves in water. - increases (Reference: Chang 17.5) 2. For each pair of substances listed here, choose the one having the larger standard entropy value at 25ºC. The same molar amount is used in the comparison. Explain the basis for your choice. (12 points) a. Li( s ) or Li( l ) - Li( l ) b. C 2 H 5 OH( l ) or CH 3 OCH 3 ( l ) - C 2 H 5 OH( l ) c. Ar( g ) or Xe( g ) - Xe( g ) d. CO( g ) or CO 2 ( g ) - CO 2 ( g ) e. O 2 ( g ) or O 3 ( g ) - O 3 ( g ) f. NO 2 ( g ) or N 2 O 4 ( g ) - N 2 O 4 ( g ) (Reference: Chang 17.9) 3. Using the data in Appendix 3 of the textbook, calculate the standard entropy changes for the following reactions at 25ºC. (8 points) a. S( s ) + O 2 ( g ) → SO 2 ( g ) 248.5 - 31.88 - 205.0 = 11.62 J/K b. MgCO 3 ( s ) → MgO( s ) + CO 2 ( g ) 26.78 – 213.6 – 65.69 = 174.69 J/K (Reference: Chang 17.11) 4. Without consulting Appendix 3 in the textbook, predict whether the entropy change is positive or negative for each of the following reactions. Give reasons for your predictions. (12 points) a. 2KClO 4 ( s ) → 2KClO 3 ( s ) + O 2 ( g ) i. Positive – change of phase from solid to gas is a significant increase in entropy b. H 2 O( g ) → H 2 O( l ) i. Negative – change of phase from a gas to a liquid is a significant decrease in entropy 1 Copyright © 2017 by Thomas Edison State University. All rights reserved.

c. 2Na( s ) + 2H 2 O( l ) → 2NaOH( aq ) + H 2 ( g ) i. Positive – change of two phases, solid to aqueous and liquid to gas, is two significant increases to entropy along with the creation of an aqueous solution. d. N 2 ( g ) → 2N( g ) i. Positive – more moles of molecules are formed increasing overall entropy even though larger molecules are broken down. (Reference: Chang 17.13) 5. Calculate Δ G º for the following reactions at 25ºC: (15 points) a. N 2 ( g ) + O 2 ( g ) → 2NO( g ) 2(86.7) – 191.5 – 0 = -181.1 KJ/mol b. H 2 O( g ) → H 2 O( l ) -237.2 + 228.6 = -8.6 KJ/mol c. 2C 2 H 2 ( g ) + 5O 2 ( g ) → 4CO 2 ( g ) + 2H 2 O( l ) 4(-394.4) + 2(-237.2) – 2(209.2) – 5(0) = -2470.4 KJ/mol (Reference: Chang 17.17) 6. From the values of Δ H and Δ S , predict which of the following reactions would be spontaneous at 25ºC: If any of the above reactions is nonspontaneous at 25ºC, at what temperature might it become spontaneous? (16 points) Reaction A: Δ H = 10.5 kJ/mol, Δ S = 30 J/K ∙ mol  Nonspontaneous – spontaneous in reverse at room temperature, spontaneous in forward at high temperatures (greater than 350K)  10.5/0.03 = 350K Reaction B: Δ H = 1.8 kJ/mol, Δ S = –113 J/K ∙ mol  Nonspontaneous – spontaneous in reverse only, at any temperature. (Reference: Chang 17.19) 7. Calculate K P for the following reaction at 25ºC: (8 points) H 2 ( g ) + I 2 ( g ) ⇌ 2HI( g ) Δ G º = 2.60 kJ/mol 2.60 = -(8.314)(298.15)ln K p ln K p = -1.05x10 -3 K p = 0.99895~1 (Reference: Chang 17.23) 8. Referring to the metabolic process involving glucose, calculate the maximum number of moles of ATP that can be synthesized from ADP from the breakdown of one mole of glucose. (8 points) C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O Δ G º = –2880 kJ/mol ADP + H 3 PO 4 → ATP Δ G º = +31 kJ/mol 2 Copyright © 2017 by Thomas Edison State University. All rights reserved.