system
Given the following post, respond as if you're commenting on Reddit:
human
Are there any materials that can exist in two or more different states at certain pressures/temperatures?

To expand on this: can these materials exist in these two different states stably? If not, why isn't this possible?
gpt
Yes materials can stably exist in more than one state at the same temperature and pressure. Some examples include vapor-liquid equilibrium where a liquid and vapor phase coexist, solid-liquid equilibrium where a solid coexists with a liquid, and solid-liquid-vapor equilibrium (aka the triple point) where all three phases coexist.