Enthalpy of Vaporization and Vapor Pressures: An Inexpensive Apparatus

An inexpensive apparatus is described for the determination of the vapor pressure of a liquid as a function of temperature for the purpose of calculating enthalpy changes of vaporization. The solid-state pressure transducer is linear above 100 torr, is useful in the range -40 to 85 °C, and is calibrated using pure water. The experimental enthalpies of vaporization for ten solvents are within ca. 0 to 13% of literature values. Two different versions of the static vapor pressure apparatus are described. Also described are a simple air thermostat and an inexpensive temperature controller (±0.1 K) based on an integrated temperature sensor. The measurement time is under three hours.