Chem 156 Examination 4

CHEM 156, Examination 4, Advanced Problems.

Instruction: Solve the following problems clearly and systematically.

1. Calculate the molar entropy of liquid chlorine at its melting point, 172.12 K, from the following data obtained by W. F. Giauque and T. M. Powell:

T/KCp/J K-1

mol-1   T/KCp/J K-1

mol-1

15 3.72 60 33.4720 7.74 70 36.3225 12.09 90 40.6330 16.69 110 43.8135 20.79 130 47.2440 23.97 150 51.0450 29.25   170 55.10

The heat of fusion is 6406 J mol-1. [Note: Use cross-section paper or graphing paper.]

2. Although expressions in terms of fugacities are exact, they are useful only if we know how to interpret fugacities in terms of actual pressures. If we write the fugacity as

f = φp

where φ is the dimensionless fugacity coefficient, then φ is related to the compression factor, Z, of the gas between p = 0 and the pressure of interest by

p

ln φ = ∫0 (Z-1)/p dp (see Atkins’ and de Paula’s Physical Chemistry, 7th Ed. for proof)

In an investigation of thermophysical properties of toluene (J. Phys. Chem. Ref. Data 18, 1565 (1989)), R.D. Goodwin tabulated (among other quantities) the compression factor, Z, at several temperatures and pressures. From the following information, compute the fugacity coefficient of toluene at 600 K and (a) 30.0 bar and (b) 1000 bar.

[Note: Use cross-section paper or graphing paper.]

Comment on the values obtained. Compare them to that of an ideal gas. Provide explanations for any observed differences.

3. In a study of the vapor pressures of chloromethane (J. Chem. Eng. Data 40, 869 (1995)), A. Bah and N. Dupont-Pavlovsky presented data for the vapor pressure over solid chloromethane at low temperatures. Some of that data is shown below:

Estimate the standard enthalpy of sublimation of chloromethane at 150 K. Take the molar volume of the vapor to be that of a perfect gas, and that of the solid to be negligible. [Note: Use Microsoft Excel.]

p/bar Z   p/bar Z0.500 0.994 12 42.4 0.471 981.013 0.988 96 50.0 0.223 762.00 0.979 42 70.0 0.265 203.00 0.969 95 100.0 0.349 205.00 0.951 33 200 0.623 62

10.00 0.905 69 300 0.882 8820.00 0.812 27   500 1.371 0930.00 0.701 77 1000 2.488 36

T/K 145.94 147.96 149.93 151.94 153.97 154.94p/Pa 13.07 18.49 25.99 36.76 50.86 59.56

Questionnaire No. ___