CHEM101: General Chemistry I

As we saw above, heating curves show us how the temperature of a substance changes as we apply heat to it. We can use heating curves to determine the phase of a substance at a given temperature.

Another graph used to determine the phase of a substance is a phase diagram. Phase diagrams show the effect of pressure and temperature on the phase of a given substance. In a phase diagram, the temperature is shown on the x-axis and the pressure is shown on the y-axis. Curved lines show where phase changes occur. Areas between the curved lines show the conditions where the substance is a solid, liquid, and gas. All phase diagrams have a similar form, making them relatively straightforward to interpret.

Watch this video to see examples of phase diagrams, and how we can determine the phase of a substance at a given temperature and pressure. Also note the triple point, melting point, boiling point, and supercritical point on the phase diagram.