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Q & A: liquid from gases

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Most recent answer: 10/22/2007
Q:
How is it that when Hydrogen and Oxygen (both gases) are mixed together they form a liquid (water) ?
- Sanat Deshpande (age 7)
Center Square Academy, Blue Bell, PA
A:

Sanat- One of the main factors that determines whether a material sticks together, as a liquid or solid, or flies apart as a gas, is how well the molecules stick to each other. Water molecules stick to each other pretty well. That's largely because there's some negative electrical charge on the oxygen and positive charge on the hydrogens. That makes the O from one molecule tend to stick to H's from others.

In O2 and H2 molecules, which make up oxygen and hydrogen gases, the two atoms are just like each other. Neither gets more or less electrical charge, so they stay uncharged. That takes away one of the main forces that pulls water molecules together, and makes it easier for O2 and H2 to stay as gases at ordinary temperature and pressure. If you cool them down enough, they both turn liquid, just as water turns to gas if it's heated.

Mike W.


(published on 10/22/2007)

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