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19 Chemical Thermodynamics Solutions to Exercises (e) vaporization: -> CS₂(g) = = = = = 89.7 = is always positive, because the gas phase occupies a greater volume, has more motional freedom and a larger absolute entropy than the liquid. (f) At the boiling point, = 0 and Tb = 320 K = 47°C. is a liquid at 298 K, 1 atm 19.112 (a) AgNO₃(s); S decreases because there are fewer moles of gas in the product. (b) is relatively large and negative, as anticipated from part (a). (c) Dissolving of can be expressed as AgNO₃(s) (aq, M) = AgNO₃(aq) - AgNO₃(s) = -101.7 - (-124.4) = +22.7 = - = -1374.8 - (-1283.7) = -91.1 kJ Dissolving AgNO₃(s) is endothermic but dissolving is exothermic (d) AgNO₃: = AgNO₃(s) = -34.2 (-33.4) = -0.8kJ = / T = / 298 = 0.0789 kJ/K = = = (-1169.6) = = - / T = [-91.1 (-28.8 / 298 = -0.209 kJ/K = (e) In general, we expect dissolving a crystalline solid to be accompanied by an increase in positional disorder and an increase in entropy; this is the case for +78.9 J/K). However, for dissolving there is a substantial decrease in entropy = -209 J/K). According to Section 13.5, ion- pairing is a significant phenomenon in electrolyte solutions, particularly in concentrated solutions where the charges of the ions are greater than 1. According to Table 13.5, a 0.1 m MgSO4 solution has a van't Hoff factor of 1.21. That is, for each mole of MgSO4 that dissolves, there are only 1.21 moles of "particles" in solution instead of 2 moles of particles. For a 1 m solution, the 608