The Secret of Shrinking Ice Cubes (phase transition)

[science_spot]

Solid, Liquid, Gas... we are all familiar with these phases of matter. However, the fun begins when matter moves between phases!  Some transitions can be seen in the world around us on a daily basis, but others are more unique, only occurring in special circumstances.

Check out the diagram below.  Some of these you are very familiar with, but some may seem a bit more obscure.  Keep in mind this subject gets infinitely more complex as physicists and materials scientists move beyond the basic phases, and study plasma and supercold/hot temperatures.  We'll keep this post focused on phase transitions you and I would reasonably come across.

 

Generally the phase transitions reflect a change in temperature, but pressure can also be a big factor in phase transitions.  In order to keep it simple, we'll assume normal atmospheric pressure for this post.  In this case, a substance moves from solid to liquid to gas with an increase in temperature, and from gas to liquid to solid with a decrease in temperature.  So where might you find some of these transitions?  The KITCHEN, of course! 

 

Solid --> Liquid

We all have seen a solid substance like ice cream MELT to a liquid (and possibly run off the counter onto the floor).  Our solid ice cubes MELT to liquid water in spiked iced tea (yummy). Our solid substance is changing to a liquid due to the increase in its temperature.  Water does this at the very predictable temperature of 0C, and since ice cream is mostly water, it requires about the same temperature to MELT.

Liquid --> Gas

When we heat the liquid water to boiling at 100C, it VAPORIZES into steam (vapor/gas).  You can see this happening during the transition. As the water gets hotter, bubbles start to form in the water.  These bubbles are gaseous water molecules, and since gas is less dense than the water, they rise, eventually escaping the water and releasing as steam into the air. The water/gas mixture is a transitional phase - not all water, but not all gas, either.

Gas --> Liquid

If you were able to catch the water vapor as it releases from the water, like in a glass bottle, you would see it CONDENSE back to liquid water as it cools.  You can see this by placing a glass cover over a pot of boiling water; the glass will soon be covered with liquid water. 

Another place youwill see this is the condensation on the outside of your cold beverage during the heat of summer. This drives me crazy because I hate to use coasters.  What is happenig is the water vapor in the air is cooling along the side of your cold beverage container and CONDENSING from the gas to a liquid.

Liquid --> Solid

Now take your water and pop it in the freezer.  You know it's going to freeze to a solid (ice)!  Better yet. make the home-made ice cream I posted about in the summer - it's a much yummy way to show about freezing and thawing.

Solid ---> Gas

The conversion of solid water (ice) directly to a gas does not usually occur at normal atmospheric pressure.  However, you may have seen this transition when watching the sublimation of dry ice. Sublimation is the process of matter changing from a solid directly to a gas.  

Dry ice is the most common example given for sublimation, but there is another one, occurring in your home!  If you own a frost-free freezer, one way it may work is by keeping the air inside very dry, so the water vapor cannot freeze on the interior freezer walls.  The fact that the air is very dry and cold allows your ice cubes to sublime right in the freezer, causing them to shrink right in their trays (which I find incredibly annoying).  Keeping them covered can dramatically reduce this occurance.

Gas --> Sold

Deposition of a gas directly to a solid may seem like an unusal occurrance in nature since few people have heard of it.  In reality, it is very common (at least around here), as this is part of the process of how snow forms.  Gaseous water vapor changes directly to ice crystals (snow) in the clouds, high above the Earth.  Another common deposition is the process of electrplating (coating surfaces with metals).

 

I hope you enjoyed this post.  I would love to hear if you have more examples of these phase transitions, particularly if they are funny :)

Tonya

AKA sunmoonstars

The Science Spot

 

[You_Are_Invited]

Sep. 29, 2009 at 4:19 AM

I saw this on the activity list today and I couldn't wait to read it. I should have read it then. It would have saved me from having to look why boiling water bubbles. Of course I would never had make the connection between shrinking ice and boiling water =D

I had no idea a frost free freezer would do that to ice cubes. I wish I had some examples for you.

[science_spot]

Sep. 29, 2009 at 6:19 AM

That's one reason I rarely keep ice around - shrunken cubes just look unappetizing to me!

(Original Poster)