# Phase transition from solid directly to gas

Why do substances like camphor experience a phase transition from solid directly to gas when they are heated? Why don't such materials behave like water, and experience a liquid phase?

• Depends where you are on the pressure-temperature phase diagram, that's all... – Jon Custer Jun 24 '17 at 3:29

Materials will sublime (go from solid directly to gas) or deposit (go directly from gas to solid) if the pressure is correct, or they will go through the "normal" three phase transition (solid to liquid to gas, or reverse) at other pressures. You can tell based on the phase diagram, which is for $CO_2$:
Additionally notice that molecules which sublime at atmospheric pressures like $CO_2$ and Camphor are non-polar or only slightly polar. This means that there will be far less inter-molecular attraction compared to a very polar molecule like water, which can engage in hydrogen-bonding; due to the low attraction between non-polar molecules, they can "fly off" a solid directly into the gas phase, since there won't be any attraction keeping them condensed in a liquid.