How does reflux condenser work? Quantifying the changes in a system: the Gibbs function All preparative chemists are familiar with the familiar Liebig condenser, which we position on top of a refluxing flask to prevent the flask boiling dry. The evaporating cools rises up the interior passage of the condenser from the flask, and thence condenses (Equation (4.20)) as it touches the inner surface of the condenser. Con- densed liquid then trickles back into the flask beneath. solvent solvent energy The energy is transferred to the glass inner surface of the condenser. We maintain a cool temperature inside the condenser by running a constant flow of water through the condenser s jacketed sleeve. The releases a large amount of heat energy as it converts back to liquid. which passes to the water circulating within the jacket. and is then swept away.