The macroscopic behavior of two microscopic unimolecular evaporation models is examined. The temperature dependences of bulk equilibrium vapor pressures deduced from the Rice-Ramsperger-Kassel (RRK) model and from the Weisskopf model, respectively, are compared. The bulk vapor pressures of sodium given by both models are compared, over a wide temperature range, with the experimental vapor pressures. The Weisskopf model is in better agreement with the experimental data than the RRK theory: from the melting temperature to the critical temperature (~ 370 K-2500 K), the vapor pressures of sodium calculated using the Weisskopf model agree with experimental values within 2%, whereas the RRK theory leads to errors of more than 40%. The Weisskopf theory satisfying the detailed balance principle, whereas the RRK theory does not, may explain this result.