Chem142 Introduction to Physical Chemistry

Transcription

1 Chem4 Introduction to hysical Chemistry Exam # (50 minutes) Name 00 points September 5, 07 Units and Constants R = 8.34 J/K*mol = L*bar/K*mol = L*atm/K*mol dm 3 = L K = C bar = 00 ka = atm atm = 0.35 ka = 760 torr L*atm = 0.35 J Equations nr an nb 0 rxn, m cal nu C w d w external wnrln Cm, C m, external i S qrev H us H S S us vap us SnC nr vap vap m, ln ln i i C S S d S C ln c x K K R K K n GRln K GGRlnQ K ln H K R ln K H S R R g ng total U nc m, H nc m, C C R m,, m H U ( ) H U Rn g H H C d H C du C d d dh Cd d cold hot GH S AU S G G H H Short Answer /3 Multiple Choice Section A / Section B / Long Answer /7 total /00 page

2 Short Answer Section (3 points) a) ( points) Identiy each o the ollowing as extensive or intensive. C,m C b) (4 points) Identiy each o the ollowing as state or path unctions. q S H w nr an c) (7 points) he van der Waals gas equation is: nb What is the physical meaning o the a parameter? What is the physical meaning o the b parameter? Under what conditions would a gas be considered ideal? (circle one choice in each o the ollowing) low / high density low / high large / small d) (8 points) An ideal gas, initially at 5 C and.0 bar, is heated to 50 C at constant volume. Fill in each o the ollowing blanks with >, <, or =. w 0 q 0 ΔH 0 ΔU 0 (circle one choice in each o the ollowing) Work was done on the surroundings by the system / on the system by the surroundings / there was no work. Heat was transerred rom the surroundings to the system / rom the system to the surroundings / there was no heat transer. e) (7 points) An ideal gas, initially at 5 C and.0 bar, undergoes an adiabatic expansion. Fill in each o the ollowing blanks with >, <, or =. Δ 0 w 0 q 0 ΔH 0 ΔU 0 ) (3 points) Regarding engines. (circle one choice in each o the ollowing): w is positive / negative / zero or one complete cycle o the engine. he eiciency o an engine is governed by the st / nd / 3 rd law o thermodynamics and is greater than / less than / equal to / equal to 0. page

3 Multiple Choice Section A ( points 3.5 points per question; no partial credit) he ollowing pertains to questions #-#6: Consider the reaction or the dehydrogenation o ethane to acetylene: C H 6 (g) C H (g) + H (g) #. Given the ollowing data (all at 5 C), determine ΔH at 5 C or C H 6 (g) C H (g) + H (g). C H 6 (g) + 7/ O (g) CO (g) + 3 H O (l) ΔH = kj/mol C H (g) + 5/ O (g) CO (g) + H O (l) ΔH = kj/mol H (g) + / O (g) H O (l) ΔH = kj/mol a) ΔH = -8.6 kj/mol b) ΔH = kj/mol c) ΔH = kj/mol d) ΔH = kj/mol e) ΔH = +8.6 kj/mol #. For the reaction C H 6 (g) C H (g) + H (g), the entropy change is likely to be: a) positive b) negative c) approximately zero #3. For the reaction C H 6 (g) C H (g) + H (g), ΔH = +39. kj/mol at 00 C and ΔH = kj/mol at 450 C. What is ΔC or the reaction? a) ΔC = +0.9 J/K*mol b) ΔC = +49. J/K*mol c) ΔC = -49. J/K*mol d) ΔC = J/K*mol e) ΔC = J/K*mol #4. For the reaction C H 6 (g) C H (g) + H (g), ΔH = +39. kj/mol and ΔS = J/K*mol at 00 C. Which o the ollowing statements is correct concerning ΔG or the reaction at 00 C? a) ΔG = kj/mol, implying the reaction is spontaneous. b) ΔG = +08. kj/mol, implying the reaction is spontaneous. c) ΔG = kj/mol, implying the reaction is non-spontaneous. d) ΔG = kj/mol, implying the reaction is non-spontaneous. e) ΔG = +08. kj/mol, implying the reaction is non-spontaneous. #5. For the reaction C H 6 (g) C H (g) + H (g), ΔG = kj/mol at -8.0 C. Calculate the equilibrium constant K at this temperature. a) 9.67*0-5 c).03*0 5 b) d). #6. For the reaction C H 6 (g) C H (g) + H (g), ΔH = +39. kj/mol at 00 C. Calculate the -work done by the reaction at 00 C. a) w = kj/mol b) w = kj/mol c) w = kj/mol d) w = kj/mol e) w = +.80 kj/mol page 3

4 Multiple Choice Section B ( points 3.5 points per question; no partial credit) #. For a certain biochemical reaction ΔG = +5.0 kj/mol. I the reaction is coupled to A hydrolysis or which ΔG = kj/mol, is the overall chemical process spontaneous? a) No, because ΔG < 0 or the overall chemical process. b) No, because ΔG > 0 or the initial biochemical reaction. c) Yes, because ΔG < 0 or the overall chemical process. d) Yes, because ΔG < 0 or the second chemical reaction. he ollowing pertains to questions #-#6: Based on this chemical reaction, answer the ollowing questions. Sulur dioxide is used as a ood preservative and in winemaking. It can be produced according to the ollowing reaction: H S (g) + 3O (g) H O (l) + SO (g) For the reaction at 5 C, ΔG = kj/mol and ΔH = -4.0 kj/mol. #. In order to shit the position o the equilibrium to the right, the reaction temperature should be: a) increased b) decreased c) there is no eect rom temperature on the equilibrium #3. In order to shit the position o the equilibrium to the right, the total pressure or the reaction should be: a) increased b) decreased c) there is no eect rom pressure on the equilibrium #4. Which o the ollowing is true regarding the absolute entropy S or O (g) at 5 C? a) S or O (g) is 0 J/K*mol, since it is an element in its standard state. b) S or O (g) is 0 J/K*mol, according to the 3 rd law o thermodynamics. c) S or O (g) is less than that or O (l). d) S or O (g) is greater than that o most solids at the same temperature. #5. I 0.00 bar o H S(g), 0.00 bar o O (g), and 50.0 bar o SO (g) are mixed with 40.0 L o liquid water at 5 C, in what direction will the reaction proceed? a) to the let b) to the right c) neither direction (the reaction would be at equilibrium) #6. he reaction is carried out within a bomb calorimeter; 0.0 mol o H S(g) reacts at 5.0 C resulting in a temperature rise o +8.3 C. I ΔU = -6.6 kj/mol or the reaction, what is the value o the calorimeter constant? a) +3.5 J/K b) +375 J/K c) +397 J/K d) J/K e) J/K page 4

5 Long Answer Section (7 points) #. (6 points) he Joule-hompson coeicient J (important in certain types o gas expansions) is equal to C Evaluate J or an ideal gas. #. ( points) Consider the reaction: SbF 5 (l) + 4 Cl (g) SbCl 3 (s) + 5 ClF (g) At 30 C, K or the reaction is.90*0-6. a) (7 points) Compute K c or the reaction at 30 C. b) (4 points) I the reaction takes place in a 00.0-L container, how many moles o Cl (g) must be mixed with 0.0 moles o SbF 5 (l) to produce.00 moles o ClF (g) at equilibrium? (Hints: Which type o equilibrium constant will be easiest to use here? What is the best way to organize inormation about moles to start the reaction and moles at equilibrium?) page 5