Problem Set 12 Chapter 19 Thermodynamics 1 Which order below is not correct for the entropy of the particular substances a SO3 SO2 b KCl NaCl c NO2 N2O d O2 O3 e CH3OH g CH3OH l 2 Which entries below should have the highest standard molar entropy a SiCl4 s b CCl4 l c CCl4 g d SiCl4 l 3 Which of the following four processes are accompanied by an increase in entropy 1 I2 s I2 g 2 2 I g I2 g 3 2 NH3 g N2 g 3 H2 g 4 Pb2 aq 2 OH aq Pb OH 2 s Choices a 1 2 b 1 3 c 3 4 d 2 4 e only 3 4 The standard molar entropy value of N2 g is 191 5 J K mol of O2 g is 205 0 J K mol and of NO2 g is 240 0 J K mol From these values we can calculate the DSo for the reaction N2 g 2 O2 g 2 NO2 g to be a 156 5 J K b 636 5 J K c 15 5 J K d 121 5 J K e 83 5 J K Note the symbol D for delta may show up differently on your printer I will use from now on 5 For a particular reaction Go is more negative than Ho This means that a So is zero b So is negative c So is positive d So is negative if Ho is positive e So is negative if Ho is negative 6 Sodium reacts violently with water according to the equation 2 Na s 2 H2O l 2 NaOH aq H2 g The resulting solution has a higher temperature than the water prior to the addition of the sodium What are the signs of Ho and So for this reaction a Ho is negative and So is positive b Ho is positive and So is negative c Ho and So are both negative d Ho and So are both positive 7 Nitrosyl chloride NOCl decomposes at high temperature The equation is 2 NOCl g 2 NO g Cl2 g at 227oC Using Ho 81 2 kJ and So 128 J K calculate the value of the equilibrium constant for this reaction a 1 60 X 10 2 b 2 1 X 10 7 c 62 8 d 4 9 X 106 e 3 20 X 109 8 Free energies of formation are a always positive b always negative c never zero d measured at 298K e more than one response above is correct 9 Go for a reaction can be calculated from 1 Go f data 2 Ho f and So data 3 equilibrium constants a only 1 or 2 or 3 b 1 2 only c 1 3 only d 2 3 only e 1 2 3 10 Calculate the value of Go for the following reaction given the standard free energies of formation listed below each ion Ag SO3 2 3 Ag 2SO3 2 Gf o kJ mol 943 77 497 a 1860 kJ b 128 kJ c 26 kJ d 369 kJ e 523 kJ 11 Which of the following statements is not true Answer e if all are true a The reverse of a spontaneous reaction is always nonspontaneous b A spontaneous reaction always moves toward equilibrium c A highly spontaneous reaction does not have to occur rapidly d Spontaneous reactions can be exothermic or endothermic 12 A reaction will be nonspontaneous under all conditions when a G is negative b H is negative and DS is positive c H is positive and DS is negative d H is positive independent of the value and sign of DS e S is positive independent of the value and sign of DH ANSWERS 1 D 2 C 3 B 4 D 5 C 6 A 7 A 8 D 9 E 10 C 11 E 12 C