# Why does water change phase so easily?

I did some undergraduate level Chemistry as part of my degree. It left me with the distinct impression that the polarity of water is responsible for its unusual phase properties: it's the only everyday substance that can exist in all three states under easily replicable conditions.

My daughter is learning about states of matter at school, and I thought this might be a fun "extra" for her homework, so I sat down to explain it to her. At which point I realised that I couldn't explain it myself. Polarity explains why water solidifies relatively easily, and why ice floats/expands - but I couldn't see/remember why it might have anything to do with transition into a gas.

So I taught her about phase diagrams instead, as a nice visual thing to take to class.

But it left me with the question: does water's polarity help explain its unusual phase properties? Or is it something else? Or are those phase properties perhaps not as unusual as I seem to remember?

• It's all about hydrogen bonding. I find @ssavec's answer most adequate. – M.A.R. Jan 19 '15 at 15:15
• I would say the reason water is the only substance that can exist in all three states under everyday conditions is that we happen to live on the one planet in the Solar system whose surface conditions are near its triple point. (Which isn't necessarily that much of a coincidence, given the necessity of liquid water for life as we know it.) – Nathaniel Jan 19 '15 at 22:13

If you compare water to "nearest" non-H-bonded analog, dimethylether, $\ce{CH_3-O-CH_3}$ you'll find, that vapor pressure of ether is much higher (500 kPa) than water (2.3 kPa).