CH301 Fall 2013 XXX Professor Name EXAM 4 25 POINTS Name KEY UT EID VERSION Questions on front and back Show work for partial credit Your work and answers must fit in the boxes provided for each question Responses outside the boxes will not be graded Consider the combustion of one mole of hydrazine N2H4 at 1 atm and 298K N2H4 l 3 O2 g 2 NO2 g 2 H2O l 1 3 points Calculate the change in the standard reaction entropy for the system S rxn nS products nS reactants S rxn 2 S H20 l 2 S NO2 g 1 S N2H4 l 3 S O2 g S rxn 2 70J molK 2 240J molK 1 12J molK 3 205J molK S rxn 620J molK 627J molK S rxn 7 J K for 1 mol of this reaction which is what we have when we combust 1 mol hydrazine OR S rxn 0 007 kJ K Total of 3 pts 1 pts for correct equation set up 2 points for correct answer or 3 pts for correct answer with some articulate work shown 2 3 points Calculate the change in the standard reaction enthalpy for the system H rxn n Hf products n Hf reactants H rxn 2 Hf H20 l 2 Hf NO2 g 1 Hf N2H4 l 3 Hf O2 g H rxn 2 286kJ mol 2 33kJ mol 1 50kJ mol 3 0kJ mol H rxn 506kJ mol 50kJ mol H rxn 556 kJ for 1 mol of this reaction which is what we have when we combust 1 mol hydrazine Total of 3 pts 1 pts for correct equation set up 2 points for correct answer or 3 pts for correct answer with some articulate work shown 3 3 points Calculate the change in standard Gibbs Free Energy for the system G rxn H rxn T S rxn G rxn 556 kJ 298k 0 007 kJ K G rxn 533 914 kJ Total of 3 pts 1 pts for correct equation set up 2 points for correct answer using the numbers provided from 1 and 2 Questions on front and back or 3 pts for correct answer with some articulate work shown 4 3 points At what temperature will this reaction become spontaneous or non spontaneous Will the reaction be spontaneous above or below this temperature 0 G rxn H rxn T S rxn 0 H rxn T S rxn 0 556 kJ T 0 007 kJ K T 556 kJ 0 007 kJ K T 79 428 57 K The reaction will be spontaneous below this temperature Total of 3 pts 1 pts for correct equation set up 1 points for correct answer using the numbers provided from 1 and 2 1 point for correct analysis of spontaneity or 3 pts for correct answer with some articulate work shown and correct analysis of spontaneity 5 3 points Will the sign on work be positive negative or zero Please explain your answer It will be positive There are fewer gas moles in the products than in the reactants The external pressure will do work ON the system and compress the system Work ngasRT 2moles 3moles 8 314J molK 298K 2 477 57 J Total of 3 pts 1 pts for correct sign 2 pts for correct logical explanation via words or through math 6 10 points Match the following terms with the appropriate definition by placing the corresponding letter in the provided blank a Enthalpy b Entropy f Internal Energy c First Law of Thermodynamics g Heat Capacity d Heat h Specific Heat Capacity j Kinetic Energy Total of 10 pts 1 pt for each response i energy of a system based on composition and position j energy of motion Questions on front and back e Work i Potential Energy b energy dispersed relative to the temperature h intensive measure of heat flow relative to temperature change a heat flow at constant pressure g extensive measure of heat flow relative to temperature change f total energy of a system d transfer of energy from a hot body to a cold body c conservation of energy e organized molecular motion across a distance Questions on front and back
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