Monday, April 23, 2018

density - Why is ice less dense than water?


The answers to this question explain that ice is less dense than water because it has a "crystal structure", but they dont explain what exactly that is and why this happens, also I saw this answer from another site stating that not all ice is less dense than water.


What is the "crystal structure" that ice has? Why is ice structured that way? Can ice be more dense than water, and if yes, how and when?



Answer




I'm sure you have seen photographs of snowflakes up close. You will notice that there are hundreds of small crystals of ice. This is the crystal structure of ice. You don't see ice cubes with a crystal structure because they freeze too fast. The water doesn't have enough time to move into the crystal lattice when you freeze the water. This web site shows how the molecules line up in the crystals.


Yes, some ice is denser than water. If you put pressure on regular ice, and give it time to rearrange, the molecules will move into a new crystal lattice which results in the ice being more dense than water. In the first ice crystal, there are spaces between some of the molecules which is not there in the second crystal structure.


With extreme pressure, you can have frozen water at 100 °C.


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