Chem 1202 Form 3 Fall 2024 Dr Gasery Exam 3 Chapters 5 and 19 Thermochemistry and Chemical Thermodynamics Instructions Use an 8 5 x 11 inch green and white scantron On Side Two of the scantron 1 Print your Last Name then First Name and bubble it in 2 Print and bubble in your complete correct LSU ID number 89 number 3 Bubble 3 in the Grade or Education box On Side One of the scantron 1 Print your name 2 Answers to the exam questions must go on side one Bubble the answers on 3 There is exactly one best answer for each question and you should NOT the scantron sheet using a pencil leave a question blank 4 On a numerical question choose the response closest to the correct answer This exam is closed notes and closed book You are not allowed to use your own scratch paper Only a scientific calculator is allowed during the exam NO graphing calculators Mark your answers in your Exam for future reference You can keep your Exam for further study Present your LSU ID and the front of your exam when submitting your scantron Useful Information and Constants The periodic table is located at the back of the exam R 8 314 0 08206 atm 101 3 J 1 L atm J mol K L mol Grxn o Hrxn o T Srxn o E q w S G Go RT ln Q Keq e Go RT q T q Cs m T q Ccal T wsys P V 1 1 Consider the following reaction 2 SO2 g O2 g 2 SO3 g rxn 196 6 kJ mol Under the The change in enthalpy at 298 K for this reaction is Ho same conditions the entropy change for this reaction is So the value of Keq for this reaction at 1500 K Assume that Ho do not change with temperature Use R 8 314 J K for the value of the gas constant a At this temperature Keq 1 64 x 109 b At this temperature Keq 2 92 x 10 10 c At this temperature Keq 3 61 x 1024 d At this temperature Keq 1 64 x 105 e At this temperature Keq 6 51 x 10 7 The correct answer should have been 7 54 x 104 credit was given back to those who got this question incorrect rxn 189 6 J mol K Calculate rxn are the same and rxn and So 2 Consider the following reaction C2H3 s 4 Cl2 g 2 CCl4 g H2 g The enthalpy change at 298 K for this reaction is Ho change for this reaction under the same conditions is So the value of Grxn at a temperature of 800 K Assume that Ho with temperature rxn 440 1 kJ mol The entropy rxn 343 26 J mol K Calculate rxn do not change rxn and So a At this temperature Grxn 165 5 kJ mol b At this temperature Grxn 311 3 kJ mol c At this temperature Grxn 542 7 kJ mol d At this temperature Grxn 492 7 kJ mol e At this temperature Grxn 140 6 kJ mol 3 Consider the following reaction 2 Na2O2 g 2 H2O l 4 NaOH s O2 g If 20 0 g of Na2O2 reacts with water how much heat in kJ is released by the reaction Ho f of the reaction is 126 kJ mol Molar mass of Na2O2 is 77 98 g mol a 29 3 kJ b 7 81 kJ c 39 4 kJ d 8 27 kJ e 16 2 kJ 4 Which of the following statements about enthalpy is FALSE a A process for which H 0 is called exothermic b A positive H corresponds to an endothermic process c The enthalpy of a reaction is equal to the heat of the reaction d Because enthalpy relates to heat the enthalpy change for a process does not depend on the path taken e When pressure is constant the change in enthalpy of a process is equal to the amount of heat transferred into or out of the system 2 5 Consider the following reaction 2 PCl3 g O2 g 2 POCl3 g For the reaction above Go rxn 452 41 kJ mol at 298 K What is the G for this reaction at 298 K given the partial pressure of 10 0 atm PCl3 9 0 atm O2 and 1 00 atm POCl3 Use R 8 314 J K for the value of the gas constant a G 156 1 kJ mol b G 469 3 kJ mol c G 643 2 kJ mol d G 801 5 kJ mol e G 147 9 kJ mol 6 When 7 50 g of solid ammonium chloride NH4Cl is dissolved in 70 0 g of water in a coffee cup calorimeter pictured to the right the temperature cools from 30 00 C to 10 27 C Calculate H in kJ mol of NH4Cl for the process The specific heat of water is 4 184 J g C a H 6 39 kJ mol b H 45 6 kJ mol c H 116 7 kJ mol d H 34 5 kJ mol e H 82 3 kJ mol 7 Which of the following will have H f 0 kJ mol a Cl2 g b CO2 g c BaCO3 s d NaBr s e C4H10 l 8 How much heat is needed in kJ to raise the temperature of 5 00 kg of water from 40 0 C to 90 C The specific heat of water is 4 184 J g C a 1046 kJ of heat is needed b 322 kJ of heat is needed c 2007 kJ of heat is needed d 1278 kJ of heat is needed e 205 kJ of heat is needed 9 Calculate E and determine whether the process is endothermic or exothermic for the following case A system absorbs 122 kJ of heat from the surroundings and does 572 kJ of work on the surroundings a E 450 kJ This process is exothermic b E 694 kJ This process is exothermic c E 694 kJ This process is endothermic d E 50 kJ This process is exothermic e E 450 kJ This process is endothermic 3 10 Which of the following molecules has the highest absolute entropy a Al s b Br2 s c Na s d NH3 g e C2H5OH g Use the following reaction and thermodynamic data for Questions 11 and 12 C2H6 g O2 g C2H4 g H2O g Ho f 84 68 kJ mol Ho f 0 kJ mol Ho f 52 3 kJ mol Ho f 241 82 kJ mol So 229 5 J mol K So 205 0 J mol K So 219 4 J mol K So 188 83 J mol K Go f 32 89 kJ mol Go f 0 kJ mol Go Go f 68 11 kJ mol f 228 57 kJ mol 2 C2H6 g O2 g 2 C2H4 g 2 H2O g 11 Is the reaction spontaneous in the forward direction a Yes b No c The reaction is at equilibrium 12 …