During a phase change, what happens to the temperature of a substance?

1 Answer
Jun 7, 2017

We don't really know, because there are two common types of phase changes...

Consider the phase diagram for #"CO"_2#:


This says that a sublimation phase change could happen, for example, at a constant #"1 atm"# by increasing the temperature past about #-78.5^@ "C"#.

That is a horizontal phase transition, with a change in temperature at constant pressure.

But we could also keep the temperature constant at #-78.5^@ "C"#, and decrease the pressure past #"1 atm"# to sublime as well.

That is a vertical phase transition, with a change in pressure at constant temperature.