It is a well known fact that water expands when it freezes, and here's one of the explanations I found on Physics SE:

Why water expands when freezes?

"The expansion upon freezing comes from the fact that water crystallizes into an open hexagonal form. This hexagonal lattice contains more space than the liquid state."

My question:

(1) According to what I've read earlier, water expands on freezing due to hydrogen bonding (the molecules exist in a cage like structure, whose breakage results in increase in volume) Could someone please explain how the two explanations are related?

I've read Solid State, Thermodynamics etc. so I'm looking for the best possible and detailed explanation possible.

(2) Can we define a coefficient of volume expansion for this freezing process? If yes, how? Would it be an experimentally determined constant (or variable quantity) or is it possible to obtain it as a function of temperature, number of molecules, etc. (related quantities)


  • $\begingroup$ 1. Not clear what difficulty you have in relating the formation of bonds to a change of density. See Floris' answer to one of the questions linked to the one you quoted. 2. Not clear what you mean by a coefficient of volume expansion in this situation. Change of state occurs at constant temperature, so it cannot be a function of temperature. Why do you think it might depend on the number of molecules present? $\endgroup$ – sammy gerbil Oct 3 '17 at 12:37
  • $\begingroup$ As an FYI, there are a number of other substances that expand upon freezing that do not involve hydrogen bonding. $\endgroup$ – Jon Custer Oct 4 '17 at 13:23
  • $\begingroup$ Please share more @Jon Custer $\endgroup$ – arya_stark Oct 4 '17 at 13:39
  • $\begingroup$ As simple examples, the elements Si, Ge, Sb, and Bi all have liquids that are denser then the solid at the melting point (which is one of the reasons Bi is a common constituent of solders and brazes). $\endgroup$ – Jon Custer Oct 4 '17 at 13:46

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