Problem Set 3b Chapters 12 13 1 When a liquid boils the liquid molecules bonds break air bubbles escape from the liquid the vapor pressure of the liquid is less than atmospheric pressure the vapor pressure of the gas is less than the vapor pressure of the liquid the vapor is made up of the same kind of molecules as the liquid 2 The normal boiling point of a liquid on a vapor pressure curve is found at the point where the temperature is equal to the pressure at any point where the pressure is less than 760 mm Hg at the point where the temperature line crosses the 760 mm Hg line in the region below the curve in the region above the curve a b c d e a b c d e 3 Which group includes only endothermic processes freezing vaporization deposition a b freezing condensation deposition c melting condensation deposition d melting evaporation sublimation e melting condensation sublimation 4 The temperature at point a is the critical point a triple point b c absolute freezing point d normal freezing point e normal boiling point 5 The temperature at point d is the critical point a triple point b absolute freezing point c d normal freezing point e normal boiling point 6 The transition from Phase I to Phase III is called 7 The normal boiling point of chloroform CHCl3 is 61 2 C At a pressure of 1 1 atm the boiling point is a melting freezing b sublimation c evaporation d condensation e expected to be a 61 2 C b 61 2 C c 61 2 C d 60 1 C e none of these 8 For a pure substance three phases are present simultaneously at 9 Mercury metal has a vapor pressure of 0 273 mm Hg at 101 C and 2 81 mm Hg at 151 C Calculate the enthalpy of vaporization of mercury R 8 31 J mol K 10 Which of the following statements are correct 1 2 3 All three phases gas liquid and solid exist at equilibrium at the triple point Above its critical temperature and pressure a substance becomes a supercritical fluid A liquid boils when its vapor pressure equals the pressure above its surface the critical point a the normal melting point b the normal boiling point c d all of these e none of these a 5 81 kJ mol b 7 00 kJ mol c 11 8 J mol d 61 4 kJ mol e 969 kJ mol a 1 only or 2 only or 3 only b 1 and 2 only c 2 and 3 only d 1 and 3 only e 1 2 and 3 all three ANSWERS 1 E 2 C 3 D 4 D 5 B 6 C 7 B 8 E 9 D 10 E