CH 201 Self Study Worksheet 4 Key 1 Answer the following questions based on this reaction and the thermodynamic data given 2HBr g Cl2 g 0 223 0 2HCl g 92 30 186 8 Br2 g 30 91 245 38 H f kJ mol S J molK 36 198 59 a Using the data above calculate H in kJ mol and indicate if the reaction is exothermic or endothermic Products Reactants H 2 H f HCl H f Br2 2 H f HBr H f Cl2 H 2 92 30 30 91 2 36 0 81 69 kJ 82 kJ 2 sf exothermic as H 0 b Using the data above calculate S in J K mol and indicate if entropy increases or decreases Products Reactants S 2S HCl S Br2 2S HBr S Cl2 S 2 186 8 245 38 2 198 59 223 0 1 2 J Kmol entropy decreases as S 0 c Calculate G at 500 K in kJ mol and indicate if the reaction is extensive or non extensive at this temperature Assume H and S are temperature independent G500 H T S 81 69 kJ 500K 0 0012 kJ K 81 09 kJ 81 kJ extensive as G 0 d Calculate K at 500 K in kJ mol and indicate if product or reactant is favored at equilibrium K e G RT e 81 09 kJ mol 0 008314 kJ molK 500K e19 51 3 0 108 product favored as K 1 e Calculate G at 500 K for conditionals below Does the reaction proceed in the forward or reverse direction PHBr 0 012 atm PCl2 0 035 atm PHCl 0 95 atm and PBr2 0 358 atm Q PHCl 2 PBr2 PHBr 2 PCl2 0 95 2 0 358 0 012 2 0 035 6 41x104 G500 G 500 RTlnQ 81 09 kJ mol 0 008314 kJ molK 500K ln 6 41x104 35 1 kJ 2 Calculate Q and compare it to K for the following conditions to indicate if the reaction proceeds forward or in reverse CH3COOH aq NO2 1 aq CH3COO1 aq HNO2 aq K 0 045 a CH3COOH 0 010 M NO2 1 0 10 M CH3COO1 1 0 M HNO2 0 50 M 0 045 K Q CH3COO1 HNO2 CH3COOH NO2 1 1 0 0 50 0 010 0 10 5 0x103 reaction proceeds in reverse b CH3COOH 0 102 M NO2 1 0 10 M CH3COO1 0 021 M HNO2 0 019 M 0 045 K Q CH3COO1 HNO2 CH3COOH NO2 1 0 021 0 019 0 102 0 10 0 039 reaction proceeds forward CH 201 Self Study Worksheet 4 Key 3a For mercury H vap 59 1 kJ mol and the normal boiling point is 357 C What is the value of S vap in J K mol Remember vaporization is Hg l Hg g H vap 59 1 kJ mol K PHg Normal BP P 1 atm at 357 C 273 630 K K630 1 atm At 630 K G 630 RT ln 1 0 G 630 0 H T S S H T 59 1 kJ mol 630 K 0 0938 kJ molK 93 8 J mol K 3b Calculate the vapor pressure of mercury at 25 C in torr Assume that H and S are temperature independent At 298 K G 298 H T S 59 1 kJ mol 298 K 0 0938 kJ molK 31 14 kJ mol PHg K e G RT e 31 14 kJ mol 0 008314 kJ molK 298K 3 47 10 6 atm 3 47 10 6 atm x 760 torr atm 0 0026 torr 4a Carbon disulfide has a H vap 28 4 kJ mol and a vapor pressure of 100 mm Hg at 5 1 C What is the value of K at 5 1 C K pCS2 1 100 mm Hg 1 atm 760 torr 0 1316 atm 4b What is value of G vap at 5 1 C in kJ mol 4c What is the value of S vap in J K mol 4d What is the predicted boiling point of CS2 in C G 268 05 RT ln K 0 008314 kJ K mol 273 15 5 1 ln 0 1316 4 5195 kJ K mol S H G T 28 4 4 5195 268 05 0 08909 kJ K mol 89 1 J K mol At 268 K G 268 H T S G 0 at bp so T H S 28 4 kJ mol 0 08909 kJ K mol 318 78 K 273 15 45 6 C 5 Two diagrams show the energies of three A particles and three B particles 1 x x2 x3 3 1 3 x 6x2 10 x3 12x4 12x5 10x6 6x7 3x8 x9 1 x x2 3 1 3x 6x2 7x3 6x4 3x5 x6 1 x2 x4 3 1 3x2 6x4 7x6 6x8 3x10 x12 a What are the energies of system A and system B 4 and 4 b How many ways can the energy of system A be distributed 6 Using 1 x2 x4 3 the coefficient in front of x4 is 6 c How many ways can the energy of system B be distributed Using 1 x x2 x3 3 the coefficient in front of x4 is 12 d Which system has the greater entropy System B has more ways to distribute and closer energy levels
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