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Crystal structure of water has opposing poles aligned; transition to gas phase appears incomplete  

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When decreasing the temp, the water molecules eventually settle to the bottom and into a formation.  Unfortunately the arrangement has most of the molecules with partial positives facing each other and partial negatives facing each other.  They also look like they are touching. If students sketch this it is going to require a lot of explanation of why it actually isn't that way, etc.  

When heating the water to 100C, more water molecules bounce off the top of the "container" but most remain in the bottom half.  Maybe I am misunderstanding but gaseous water should be expanding and filling the container more uniformly.

These problems pertain to Unit 1, Sim 3.

This topic was modified 5 months ago 2 times by Rachel Yim
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Part of this question has been addressed in a separate post here: https://connchem.org/community/bug-reports/orientation-of-water-molecules/

The second part of your question about boiling of water is also related to concerns raised on that post. In particular, the simulations use physical constants that are from tabulated data sources. The enthalpy of vaporization of water is 40kJ/mol whereas the enthalpy of fusion is around 6kJ. That means at the same heat rate transfer, it takes about 6.5x as long for water to boil as to melt. The complete phase transition occurs if you run the simulation for enough time.

This post was modified 5 months ago by Dane DeSutter

Postdoctoral Research Associate
Simulation Developer

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