CHM 1220 In-Class Activity: Thermodynamics & Solutions Review Fall 2017 ANSWERS 1. Estimate the molar heat of vaporization of a liquid whose vapor pressure doubles when the temperature is raised from 85 °C to 95 °C. 2. Hydrogen gas (H2) is not abundant in nature but is a useful reagent in the synthesis of liquid methanol from gaseous carbon monoxide. (The mixture of H2 and CO is often referred to as syngas and is a commonly used in industrial chemistry processes). Using the provided thermodynamic data, predict under what temperature conditions this reaction is spontaneous: 2 H2(g) + CO(g) → CH3OH(l) Substance ∆Hf °(kJ/mol) S° (J/mol·K) H2(g) 0 130.6 CO(g) –110.5 197.7 CH3OH(l) –238.7 126.8 P1 = P1 T1 = 85 °C = 358 K T2 = 95 °C = 368 K P2 = 2P1 ΔHvap = ? Clausius-Clapyeron equation relates: vapor pressure, temperature, and molar heat of vaporization. Rearrange to isolate ∆Hvap, plug in values Knowns & Unknowns: 12vap2111lnTTRHPP molkJ 92.75molJ 10921.75K 3581K 36812lnKmolJ314.811ln3111221vapPPTTPPRHCHM 1220 In-Class Activity: Thermodynamics & Solutions Review Fall 2017 3. When one mole of solid ammonia melts at its normal melting point, -33.34 °C, in a room maintained at 25.00 °C, the entropy change of the surroundings is -18.96 J/K. Estimate the molar entropy of fusion of ammonia at -33.34 °C. 4. The vapor pressure of benzene (C6H6, 78.12 g/mol) at 25 °C is 0.1252 atm. What is the change in the vapor pressure when 10.00 g naphthalene (C10H8, 128.2 g/mol) is dissolved in 0.2000 kg C6H6.CHM 1220 In-Class Activity: Thermodynamics & Solutions Review Fall 2017 5. An aqueous solution of KI has a freezing point of -1.95 °C and an osmotic pressure of 25.0 atm at 25.0 °C. Assuming that KI completely dissociates in water, what is the density of the solution? 6. Ethylene glycol is used in automobile radiators as an antifreeze. Use the following information to determine the freezing point of an antifreeze solution made by mixing 2.5 L of ethylene glycol with 2.5 L of water. Ethylene glycol is essentially nonvolatile and it does not dissociate in water. molar mass of ethylene glycol = 62.1 g/mol density of ethylene glycol = 1.11 g/mL density of water = 1.00 g/mL Kf for water = 1.86°C kg/mol mKTff×=Dglycol ethylene mol 69.44glycol ethylene mol 62.1glycol ethylene mol 1glycol ethylene mL 1glycol ethylene g 11.1L 1mL 1000 glycol ethylene L 2.5=´´´÷÷øöççèæ×÷÷øöççèæ×=D waterkg 2.5glycol ethylene mol 4.694molkgC 86.1obT waterkg 5.2g 1000kg 1 watermL 1 waterg 00.1L 1mL 1000 water L 2.5=´´´C2.33o=C33C2.33C0 ooo-=-=fffTTTD-= watermixture (where m is the molality of ethylene