Question

4. Liquid ammonia has a vapor pressure of 109 mm Hg at-66°C and a heat of vaporization of 2.46 x 10 J/mol. a) Estimate the normal boiling point of ammonia. b) Estimate the ratio of the vapor pressure at -66°C to that at -45°C

Answer 1

Initi al temperature of the ammonia, T-66 C +273 207 K Pressure of the ammoni a at T,R= 109 mmHg At normal boiling point, pressure of liquid becomes equal to the atmospheric pressure (1 atm or 760 mmHg or 760 torr) Normal boiling point of the ammonia = T Pressure of the ethanol at T= 760 mmHg Heat of vaporization of the ammonia, AH 2.46x10 J/mol According to Clausius-Clapeyron equation PAH1 In 760 mmHg In 2.46x10 J/mol 8.314 JK mol207 K T 1 1 109 mmHg 2.46x 10 J/mol 8.314 JK mol207 K T 1 1 1.94 1 1 0.000656 K1 207 K T 0.00483 K~1-- =0.000656 K-1 1 0.004174 K T 240 K-273 =33 C Thus, boiling point of ammonia is -33C Initi al temperature of the ammonia, T Pressure of the ammonia at T= R 66C +273 207 K Final temperature of the amm onia, T, =-45° C +273 228 K Pressure of the ammonia at T= P Gas constant, R= 8.314JKmol Heat of vaporization of the ammonia, AH= 2.46x104 J/mol According to Clausius-Clapeyron equation AH1 In P AH 1 In 2.46x10 J/mol 8.314 JKmol207 K 228 K 1 1 PAgeC1.32 PAC 32 3.74 PC 1 = 0.267 3.74 Pagc