States of Matter Phase Diagram (2D)

This 2D companion plots water's actual pressure–temperature phase diagram: a solid region, a liquid region and a gas region separated by three real boundary curves — the Clausius–Clapeyron sublimation curve, the anomalous negative-slope melting curve, and the vaporization curve that terminates at the critical point. Drag the crosshair (or the temperature and pressure sliders) anywhere on the log-pressure chart and the live readout reports the exact phase at that point, flashing a transition label the instant the state point crosses a boundary line. The triple point (0.01 °C, 0.006 atm), where solid, liquid and vapor coexist, and the critical point (374 °C, 217.7 atm), beyond which liquid and gas become indistinguishable as a single supercritical fluid, are both marked. Unlike almost every other substance, water's solid–liquid boundary tilts toward lower temperature as pressure increases — because ice is less dense than liquid water, squeezing it melts it, the same anomaly that lets an ice skate glide and a glacier flow — the same physics explored in the site's interactive 3D version of this demonstration.