This always confuses me, is it cold that expands and heat contracts?
or the other way around, cold contracts & heat expands?
or as steam & ice spikes suggest, both steam & ice spikes expand? (free energy?)
In: Chemistry
Water is somewhat special in that it is most dense (smallest) at 4 degrees Celsius. If you make it colder or hotter than that it expands. Most everything contracts the colder it gets.
If you had a cube of ice at zero degrees and started to heat it it would actual condense until it gets to 4 degrees rather than expanding.
It’s a pretty rad liquid.
In general, heat expands and cold contracts. Water is unusual in that, as it forms into solid ice crystals, that crystalline structure results in it expanding rather then contracting. But this is the only point at which water is an exception. Starting with temperatures just a little bit above freezing and hotter, liquid and gaseous water expand in heat and contract in cold. The density of ice also continues to contract as it grows colder.
> is it cold that expands and heat contracts?
No, it’s normally the reverse. Water will expand when it heats, but also expands when it freezes because of its crystalline structure as a solid, so it’s an exception.
Cold contracts and heat expands. As an object gets hotter, the atoms get more excited and move around more, causing expansion.
Water ice is actually an exception to the rule, normally substances are more dense in their solid phase than in their liquid phase, but ice is actually less dense than liquid water. This is because when water freezes, it creates an ordered crystal structure where the hydrogen atoms bond with the oxygen atoms in other water molecules. When they do this, the water molecules becomes further spaced apart and the density decreases. [Here’s a great picture of what I mean.](https://hi-static.z-dn.net/files/d9b/195996d71f11abd8a9b09a312247e608.jpg)
The reason ice crystals expand has been explained handily by others here (i.e. the ordered crystal structure of ice is actually less dense than the randomly-jumbled orientation of liquid water molecules).
The reason steam creates pressure is that steam is a gas, and gases always expand to fill the available space. If the gas is within a flexible container, like a balloon, the gas will push outwards on the sides of the container and make it expand. If the gas is inside a rigid container, like a metal boiler, it will still push against the outside of the container, which will not expand, but will cause the gas to push back against itself. This is essentially what pressure is – gas molecules pushing against everything.
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