Exam 2 Spring 2018 BCH Physical Chemistry with a Biological Focus Professor Jeff Yarger

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1 Exam 2 Spring 2018 BCH Physical Chemistry with a Biological Focus Professor Jeff Yarger Feb 4-5, 2018 DUE Monday, Feb 5, 2018 by 9:00 PM (UTC-7). Turn in completed exam as a single PDF document into the assignment link on ASU Blackboard. Please make sure the completed exam is organized, self-contained and legible. Name: (as recorded on ASU Blackboard) ASU ASU ID: There are 6 multiple-choice questions and 6 numerical problems. Pick 5 multiple-choice questions and 5 numerical problems to work on this examination, for a total of 10 questions. The exam is worth a total of 100 points. Each multiple-choice question is worth 5 points and each numerical problem is worth 15 points. Please record your answers in the summary area on this first page of the exam. If you do provide more than 5 answers on the multiple-choice section, then the first 5 answered will be graded. If you provide more than 5 answers on the numerical section, then the first 5 will be graded. Please completely fill in ONE of the bubbles below for the multiple-choice questions and fill in the blank with one numerical answer and the associated units in the spaces below for the numerical problems. Answer Summary 1. a b c d e Multiple Choice Points (25 possible): 2. a b c d e (Answer 5 of the 6 questions) 3. a b c d e 4. a b c d e 5. a b c d e 6. a b c d e 7. Numerical Problem Points (75 possible): 8. (Answer 5 of the 6 questions) Total Points (100 possible):

2 1. Which of the following real gases has the largest isobaric heat capacity, Cp: a) He b) Rn c) N2 d) XeF2 e) all gases have the same heat capacity 2. Predict the change in entropy (DS) for the following reaction (D is used for deuterium, 2 H): ND4Br (s) ND3 (g) + DBr (g) a) Positive b) Negative c) Near Zero d) Exactly Zero e) none of the above 3. The values of q, w, DU and DH for the freezing of acetone at 1 atm and its normal melting point is: q w DU DH a) positive positive zero negative b) negative negative positive negative c) negative positive negative negative d) negative zero zero negative e) positive negative negative positive 4. What is the change in entropy (DS) of g of water, when it is heated from room temperature (25.0 o C) to body temperature (37.0 o C) at 1.0 atm? a) +2.8 J K -1 b) -2.8 J K -1 c) 0 J K -1 d) J K -1 e) J K -1 Page 2

3 5. When 2.0 moles of oxygen gas (O2) is heated at a constant pressure of 1.2 atm, its temperature increases from 260 to 285 K. Calculate the change in internal energy (DU) for this process. a) 1.5 kj b) -1.5 kj c) -1.1 kj d) 1.1 kj e) 2.2 kj 6. A quantity of 80 g of supercooled water at o C is mixed with 160 g of water at 95.0 o C. Calculate the entropy change (DS) for the system (the entire system being all the mixed water). a) 1.5 J/K b) -1.5 J/K c) 5.9 J/K d) -5.9 J/K e) 16.6 J/K Page 3

4 7. As accurately as possible, determine the molar entropy change when liquid water at 2 o C is taken isobarically to steam (vapor) at 950 o C. (B) What is the difference in the calculated molar entropy change (ΔS) when using the (i) explicit temperature dependence heat capacities, versus just taking the values at 2 o C and 950 o C and assuming (ii) temperature independent heat capacities? [Report the molar entropy change in units of J/Kmol] Page 4

5 8. Over the last few years, cannabis seems to be a growing social and medical topic. The active pharmaceutical ingredient (API) in cannabis plant and associated extracts is the general class of chemical compounds called cannabinoids. The most notable cannabinoid is the phytocannabinoid tetrahydrocannabinol (THC), the primary psychoactive compound in cannabis. The majority of cannabinoids produced from the cannabis plant are found in a carboxylic acid form. This includes THC, which is actually found as tetrahydrocannabinolic acid (THCA) in living cannabis plants. The process of going from THCA to THC is decarboxylation. Calculate the equilibrium constant at room temperature for the decarboxylation of THCA. Page 5

6 9. What is the ph of pure water when it is supercooled to -25 o C? [Put a box around your final answer] Page 6

7 10. What are the concentrations of all species in a mm solution of histidine at a ph of 7.4? [Put a box around your final answers] Page 7

8 11. When you put water in your freezer to make ice, it is common for this water to supercool before freezing into ice. A supercooled liquid is defined as a liquid that has a temperature below its freezing point. Let s look more closely at the thermodynamics of this common process that happens in your freezer. Calculate the change in enthalpy (ΔH) and entropy (ΔS) for the process of taking 1.0 ml supercooled liquid water (H2O (l)) at a temperature of -25 o C (initial state of the system) and having it crystalize into ice (H2O (s)) with a final temperature that is the same as the set point on your freezer (final state of the system). Students will be provided a list with the set point for their freezer, which can vary between -20 o C and -80 o C (this is the common temperature range of most standard deep freezers). [Put a box around your final answers for ΔH and ΔS] Page 8

9 12. The sequestration of carbon dioxide is critical to reducing greenhouse emissions. Taking a lesson from planet earth, which stored carbon dioxide as alkali and alkaline earth metal carbonates over geological time scales, let's determine which alkaline earth metal oxide most stably stores carbon dioxide as a carbonate. So, consider the decomposition of group II (alkali earth) solid carbonate, i.e, solid beryllium carbonate, magnesium carbonate, calcium carbonate and barium carbonate (we ll skip strontium carbonate) to form solid metal oxides and gaseous carbon dioxide. (A) Calculate the temperature at which the decomposition is thermodynamically favorable under standard pressure conditions. (B) Which of the group II carbonates would you pick to most stability sequester carbon dioxide? Page 9