Trouton's rule is one of the most useful, even if approximate, empirical observation about phase transitions. It states that the entropy of vaporization is about 10kB per particle. The rule works particularly well for weakly interacting molecules, such as those of a noble gas, but not so well for water among other substances. Assuming the rule is exact, estimate the molar enthalpy of evaporation for Argon (in kJ/mol), whose boiling point is 87.15K.