SaulsAll t1_j78b80m wrote on February 4, 2023 at 9:10 PM

Your thought is in the right direction: raising temp without increasing volume is going to raise pressure. And a higher pressure is going to mean it take more heat for water to change phase from liquid to gas. The phase diagram for water is what is important here. I think though this might be a better question for r/askscience, especially when hypothesizing an unbreakable container or an unlimited amount of heat.

Edit: Looking at other charts, there seems to be a region called supercritical fluid

pozoph t1_j78mrxn wrote on February 4, 2023 at 10:35 PM

With that sort of container, water would rise in pressure at an absurd level while heating (with thermal expansion), so the question would be
"will it freeze" more than "will it boil"

SaulsAll t1_j78ok43 wrote on February 4, 2023 at 10:49 PM

Superhot ice sounds pretty cool. How does water form a solid if there is no room to expand into the crystalline structure?

pozoph t1_j78q9sl wrote on February 4, 2023 at 11:02 PM

With pressure it would form ice VII as shown in the diagram you posted, that expand less than the ice we know from everyday. The elasticity of both liquid and solid water would set pressure at a fixed volume, exactly for the same reason the pressure would increase when heating.