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The normal boiling point of Br2(l) is 59.47 oC. Estimate Hovapn of bromine. Compare your result with a value based on data from Appendix C.
Trouton's Rule suggests that Hovapn = 87 J/molK×Tbp = (87)(273.15 + 59.47) = 29000 J/mol = 29 kJ/mol.
To use the data from the Table of Thermodynamic Quantities, use the reaction:
with Hfo (Br2(l)) = 0 kJ/mol and Hfo (Br2(l)) = 30.91 kJ/mol so Ho = Hovapn = [30.91]  = 30.91 kJ/mol.
Given the approximate nature of Trouton's Rule, the estimate and the experimental value are remarkably similar.