230_Sp17_PREP_FE_key - CHEM 230 Sp17 PREP Final Exam KEY p1 28 Formic acid will decompose to hydrogen and carbon dioxide as shown in the following

230_Sp17_PREP_FE_key - CHEM 230 Sp17 PREP Final Exam KEY p1...

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CHEM 230 Sp17 PREP Final Exam KEY p1 16 28) Formic acid will decompose to hydrogen and carbon dioxide as shown in the following reaction:HCOOH(g)--> CO2(g)+ H2(g) a) At the start of the reaction (time = 0), only formic acid is present. The rate of the reaction is monitored by measuring the totalpressure in the reaction container as shown in the data table below. The pressure of HCOOH was determined and the three plots shown below(PHCOOHvs. time; ln PHCOOHvs. time; 1/PHCOOHvs. time) were created. Write out the rate law for the reaction including the value and units of k.b) At the start of the reaction (time = 0 s), only formic acid is present. Using data from the data table, find the partial pressures of each HCOOH(g), CO2(g),and H2(g)at t = 300 s. Time (s) P total (torr) 0 220 50 324 100 379 150 408 200 423 250 435 300 435 rate (torr/s) = 0.0127 1/s P HCOOH 4 pts 1st order 4 pts P HCOOH instead of [] 4 pts value k 4 pts units of k (should match order) HCOOH (g) --> CO 2(g) + H 2(g) I 220 0 0 C -x + x +x End 220-x x x P total = 220torr -x + x+x = 435 torr x = 435-220 = 215 P HCOOH = 220-215 = 5 torr P HCOOH = torr 5 12 P CO2 = torr 215 P H2 = torr 215 ! # $%&'()* + ,'-&(' $)% % )% ,%% ,)% -%% -)% % )% ,%% ,)% -%% -)% .%% .)% ! "#$%%#& "()**& +,- ".& ! #$%%# "()**& /.0 +,- ".& ! # $ $$$%& ' $($)*+ '$($, $ $($, $(- $(-, $() $(), $ ,$ -$$ -,$ )$$ ),$ .$$ .,$ !"# $%&''%( $!"*+,,( -./ $0( !"# %&''% $!"*+,,( 102 -./ $0( ! # $%&%'()* + ,&-.'/ % ' ( - 0 , / % ,% '%% ',% (%% (,% -%% -,% !"$ %&'((&) %*+,,) -./ %0) !" $ &'((& %*+,,) 102 -./ %0) Data Table: 4 pts 4 pts 4 pts
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CHEM 230 Sp17 PREP Final Exam KEY p2 28 (cont'd from page 6) HCOOH (g) <--> CO 2(g) + H 2(g) HCOOH (g) CO 2(g) H 2(g) Δ H o f (kJ/mol) -378.7 -398.51 S o m (J/(mol K)) 218.76 213.79 130.7 (Circle one) YES NO Justify your answer with a numerical explanation using the thermochemical data in the box below. c) Has the system reached equilibrium at time = 300 s? Δ H o rxn = ΣΔ H o f (products) − Δ H o f (reactants) Δ H o rxn = 1 molCO 2 398.5 kJ mol % & ' ( ) * + 1 molH 2 0 kJ mol % & ' ( ) * + , - . / 0 1 molHCOOH 378.7 kJ mol % & ' ( ) * Δ H o rxn = 19.81 kJ Δ S o rxn = ΣΔ S o f (products) − Δ S o f (reactants) Δ S o rxn = 1 molCO 2 213.79 J Kmol % & ' ( ) * + 1 molH 2 130.7 J Kmol % & ' ( ) * + , - . / 0 1 molHCOOH 218.76 J Kmol % & ' ( ) * Δ S o rxn = 125.72 J K Δ G o rxn = Δ H o T Δ S o rxn = 19.81 kJ 298 K 125.72 J K $ % & ' ( ) 1 kJ 1000 J $ % & ' ( ) Δ G o rxn = 57.27 kJ Δ G o = RT ln K 57.27 kJ = 8.314 J Kmol $ % & ' ( ) 298 K ( ) ln K 23.11 = ln K e 23.11 = 1.09 x 10 10 = K Q <K d) This reaction is spontaneous at ( Circle one) ALL NO LOW HIGH temperatures. e) More product will be made if the reaction is run at (Circle one): HIGH LOW temperatures. match signs of Δ H and Δ S Δ H negative, larger K at lower T 4 pts 4 pts 4 pts 4 pts 4 pts Q in pressure 4 pts Q in bar 4 pts match explanation 28 4 4 Q = P CO 2 P H 2 P HCOOH = 215 torr 1 atm 760 torr " # $ % & ' 1.01325 bar 1 atm " # $ % & ' ( ) * + , - 215 torr 1 atm 760 torr " # $ % & ' 1.01325 bar 1 atm " # $ % & ' ( ) * + , - 5 torr 1 atm 760 torr " # $ % & ' 1.01325 bar 1 atm " # $ % & ' ( ) * + , - Q = 12.32 Assume 298K.
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CHEM 230 Sp17 PREP Final Exam KEY p3 20 29) Solid ammonia (NH 3 ) has a density of 0.82 g/mL and a melting point of -78 o C. Liquid ammonia has a density of 0.68 g/mL and a boiling point of -33.5 o C. What is the sign of the following properties when ammonia freezes : a) The sign of work for freezing NH 3 is: (Circle one): - + 0 cannot determine b) The sign of q for freezing NH 3 is: (Circle one): - + 0 cannot determine c) The sign of Δ T for freezing NH 3 at -78 o C is: (Circle one): - + 0 cannot determine d) The sign of Δ U for freezing NH 3 at -78 o C is: (Circle one): - + 0 cannot determine f) On the graph below sketch the curve of molar entropy vs. temperature for NH 3 from -100 o C to 20 o C.
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