Heat – Phase Transition and Critical Temperature

Observe the phase transition at the critical point.

The experiment investigates the behavior of sulfur hexafluoride close to the critical temperature. The critical temperature of this substance is Tc = 318.7 K and the critical pressure is
pc = 37.6 bar. The substance is enclosed in a pressure chamber designed so that hot water or steam can flow through the mantle. The dissolution of the phase boundary between liquid and gas while heating the substance, and its restoration during cooling, are observed in projection on the wall. As the system approaches the critical point, the substance scatters short-wave light particularly intensively; the entire contents of the pressure chamber appears red-brown. This critical opalescence is due to the variations in density, which increase significantly as the system approaches the critical point.

Pressure chamber
Lamp housing with cable
Bulb 6 V/30 W, E14, set of 2
Aspherical condenser with diaphragm holder
Transformer 6/12 V
Lens in frame, f = +100 mm
Small optical bench
Stand base V-shape, large
Leybold multiclamp (3)
Stirring thermometer, -30 ... +110 °C
Steam generator
Silicone tubing, 7 mm diam., 1 m (2)
Beaker DURAN, 400 ml, squat