As the temperature increases and liquid water changes to gas, are ALL the hydrogen bonds broken or they are just weaker?
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1$\begingroup$ Does this answer your question? Hydrogen Bonding in Water Phase Changes $\endgroup$– Nilay GhoshCommented Dec 14, 2022 at 4:00
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3$\begingroup$ Fun fact: The lack of hydrogen bonds explains why steam causes much worse burns that boiling water. Steam contains all the energy used to break the hydrogen bonds in water, so when steam hits your face you first absorb the energy the steam has taken up from breaking the hydrogen bonds it its liquid state. Then, in an exothermic reaction, steam is converted into liquid water and heat is released. This heat adds to the heat of boiling water as the steam condenses on your skin. $\endgroup$– Nilay GhoshCommented Dec 14, 2022 at 4:03
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Under commonly encountered conditions in industrial applications, essentially all hydrogen bonds are broken. Only at high pressures is hydrogen bonding likely to occur.
What happens is something of a Catch-22. If hydrogen bonding in water is significant, then it tends to form cross-linked structures because each molecule can both donate and accept two bonds, so the hydrogen bonding tends to form cross-linked structures that condense into a liquid. So to generate steam at near-atmospheric pressure you need enough thermal energy (temperature) to essentially break all the hydrogen bonds at once. Only at high pressure, where the gas becomes denser and more like a liquid, can hydrogen bonding become evident in the gas phase.
We may compare this with hydrogen fluoride, where chainlike structures form instead of cross-linked ones because each molecule donates and accepts only one hydrogen bond. The chainlike structures can be supported in the gas phase, so hydrogen fluoride gas can show hydrogen-bonded oligomers at relatively low pressures. See here.
answered Dec 13, 2022 at 15:29