The knowledge and understanding of fluid phase equilibrium is indispensable for the design of a wide range of chemical processes, and as such is a cornerstone of the undergraduate chemical engineering curriculum. In the study of phase equilibrium, early attention is often devoted to use of the Clapeyron equation. Starting with our fundamental thermodynamic relationships and criteria for phase equilibrium, the Clapeyron equation presents the opportunity to make reasonable assumptions to obtain a simple expression capable explaining the linearity of a plot of the log vapor pressure versus inverse temperature. Unfortunately, the assumptions made are often not appropriate and may cause confusion among students.