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Week 6 Key Practice Problems

Week 6 Key Practice Problems - CHEMISTRY 201X Practice...

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CHEMISTRY 201X September 24-28, 2007 Practice Problems (50) At its melting point (624 ° C), the density of solid plutonium is 16.24 g/cm 3 . The density of liquid plutonium is 16.66 g/cm 3 . A small sample of liquid plutonium at 625 ° C is strongly compressed. Predict what phase changes, if any, will occur. The density of the solid is less than that of the liquid. Therefore, by applying pressure, there will be no phase change to the solid at first. At very high pressures, we do anticipate a change to the solid state. (51) The following table gives several important points on the pressure-temperature diagram of ammonia: p (atm) T (K) Triple Point 0.05997 195.42 Critical Point 111.5 405.38 Normal Boiling Point 1.0 239.8 Normal Melting Point 1.0 195.45 (a) Use this information to sketch the phase diagram of ammonia. (b) The van der Waals constants for ammonia are 4.170 L 2 atm/mol 2 and 0.03707 L/mol. Estimate the critical temperature and critical pressure for ammonia and compare your results with the data in the table. T c = 8a/27Rb = 406.0 K p c = a/27b 2 = 112.4 atm The agreement with experiment is quite good. Both are slightly overestimated. (c) Estimate the critical density (g/cm 3 ) of ammonia.
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