Chapter 16: Spontaneity, Entropy, and Free Energy (CHEM 2C) 16.1 Use the values of standard molar entropies in Appendix to calculate the entropy change at 25°C and one atmosphere pressure for the reaction of hydrazine with hydrogen peroxide This explosive reaction has been used for rocket propulsion Do you think the reaction is spontaneous? The balanced equation for the reaction is N2H4(l) + 2H2O2(l) - > N2(g) + 4H2O(g) ǻH0rxn = - 642.2 kJ/mol reaction 16.2 Using the Appendix, calculate the standard entropy of reaction of mol of propane at 25oC: C3H8(g) + 5O2(g) -> 3CO2(g) + 4H2O(l) 16.3 At 298 K, the formation of ammonia bas a negative ǻ6osys: N2(g) + 3H2(g) - > 2NH3(g) ǻ6osys = - 97 J/K Calculate ǻ6univ and state whether the reaction occurs spontaneously at this temperature 16.4 Calculate ǻ6o at 25°C for the reaction : CH4(g) + 2O2(g) - > CO2(g) + 2H2O(g) given the standard entropy values: CH4(g) 86 J/K mol CO2(g) 214 J/K mol O2(g) 205 J/K mol H2O(g) 189 J/K mol 16.5 Does the combustion of methane with oxygen occur spontaneously at 298K? CH4(g) + 2O2(g) - > CO2(g) + 2H2O(g) o o ǻ6 sys = - J/K ǻ+ f(CH4)= - 75 kJ ǻ+of(CO2)= - 393.5 kJ ǻ+of(H2O)= - 242 kJ 16.6 Mercury has an enthalpy of vaporization of 58.51 kJ/mol, and an entropy of vaporization of 92.92 J/K mol What is the normal boiling point of mercury? Hg(l) - > Hg(g) o ǻ+ = - 58.51 kJ/mol ǻ6o = 92.921 J/mol 16.7 &DOFXODWHǻ*orxn at 25oC for the following reactions: 1/ CH4(g) + 2O2(g) > CO2(g) + 2H2O(g) 2H2S(g) + SO2(g) < - > 3S (s) + 2H2O(g) give the values for the standard free energies of formation: CH4(g) - 51 kJ/mol H2S(g) -33 kJ/mol CO2(g) - 394 kJ/mol H2O(g) - 229 kJ/mol Nguyen Tien Thao, Faculty of Chemistry, Hanoi College of Science, VNU 19 - Le Thanh Tong, Hoan Kiem, Hanoi, Vietnam Email: nguyentienthao@gmail.com SO2(g) - 300 kJ/mol 16.8 What is ǻ*o for the autoionization of water at 25°C? 16.9 The oxidation of SO2: 2SO2(g) + O2(g) - > 2SO3(g) is too slow at 298 K to be useful in the manufacture of sulfuric acid To overcome this low rate, the process is conducted at an elevated temperature (a) Calculate K at 298 K and at 973 K (ǻ*o298 = -141.6 kJ/ mol for reaction as written; using ǻ+o DQGǻ6o DYOHDDW.ǻ*o973 = -12.12 kJ/ mol for reaction as written) (b) In experments to determine the effect of temperature on reaction spontaneity, two sealed containers are filled with 0.500 atm of SO2, 0.0100 atm of O2, and 0.100 atm of SO3 and kept at 25°C and at 700.oC In which direction, if any, will the reaction proceed to reach equilibrium at each temperature? ( c) Calculate ǻ*for the system in part (b) at each temperature 16.10 Diatomic nitrogen and oxygen molecules make up about 99% of all the molecules in reasonably “unpolluted” dry air Evaluate using ǻGo for the following reaction at 298 K, ǻG0f values from Appendix Is the standard reaction spontaneous? N2(g) + O2(g) - > 2NO(g) (nitrogen oxide) 16.11 Make the same determination as in Problem 11.10, using heats of formation and absolute entropies rather than free energies of formation 16.12 Use the thermodynamic data in Appendix to estimate the normal boiling point of broine, Br2 Assume that ǻ H and ǻ S not change with temperature 16.13 Mercury(II) sulfide is a dark red mineral called cinnabar Metallic mercury is obtained by roasting the sulfide in a limited amount of air Estimate the temperature range in which the standard reaction is product-favored using data in Appendix HgS(s) + O2(g) > Hg(l) + SO2(g) 16.14 Estimate the temperature range for which the following standard reaction is productfavored SiO2(s) + 2C(graphite) + 2Cl2(g) > SiCl4(g) + 2CO(g) Additional problems: Chapter 16: 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 81, 83, 85, 87 Complete at leat ….%, Deadline: … Nguyen Tien Thao, Faculty of Chemistry, Hanoi College of Science, VNU 19 - Le Thanh Tong, Hoan Kiem, Hanoi, Vietnam Email: nguyentienthao@gmail.com