A compound has TC = 500 K, PC = 5 MPa and ? = 0.4. The compound is known to have Psat = 2 kPa and ?Hvap = 30 kJ/mol at T = 250 K. No other data is available. Which of the following is the most accurate way to estimate the vapor pressure of this compound at 400 K?
A. The Clausius-Clapeyron equation
B. The shortcut equation
C. The Antoine equation
D. The van der Waals equation
E. None of the above is even possible with the given information.
A. Incorrect. Clausius-Clapeyron directly relates two boiling temperatures and pressures with the heat of vaporization but this is too large a temperature range over which to assume the heat of vaporization is constant.
B. Correct. At Tr=0.8 shortcut is preferred over Clausius-Clapeyron.
C. Incorrect. The Antoine parameters A, B and C are not known.
D. Incorrect. We can find the two van der Waals constants (a and b) since we know the critical point, but the van der Waals equation does not typically model vapor pressures at all accurately.
E. Incorrect. At least one is possible.
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