Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Making Ice - Cutting Back on Bubbles

Learn more physics!

Most recent answer: 10/22/2007
Q:
If you fill an ice tray with hot water and one with cold water. Which will freeze the fastest and why. which will melt faster. I have heard the hot water ice cube is a more solid cube and will have fewer air bubbles than the cold water ice cube. Is this true and why? Thank you.
- Taelin (age 7)
Puget Sound Christian, Tacama, WA
A:
Taelin -

One question at a time... First, which freezes faster - cold or hot water? We've actually answered this question already, so check out . And now to your second question...

It sounds to me like you've 'heard' correctly. Hot water will (at least in theory) make more solid ice cubes with less bubbles. The reason for this has to do with how bubbles come about in ice in the first place. All water has at least some air disolved in it. When you cool the water down to freeze it, the disolved air forms bubbles in the ice. So the amount of bubbles you get in the ice really depends on how much air there was disolved in the water in to start off with.

The warmer a gas is, the less likely it is to stay disolved. This actually makes sense if you think about it. Gas molecules normally have a lot of energy. This is what makes them move around so much. But if they get disolved in water, they have 'less room to move'. The warmer they are, the more energy they have, and the more they want to move around. By coming out of solution and going into the air, they aren't as confined as when they're disolved, so it's easier for them to move around.

So when you heat up water, you lose a lot of the air that would otherwise be disolved in it. Hence, when you start off with hot water, you get less bubbles in the ice.

-Tamara

(published on 10/22/2007)

Follow-up on this answer.