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Name: Will F.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 2/22/2004

One of my students asked me under what conditions hydrogen gas and oxygen gas can come together to form water. In particular, he wanted to know the exact process by which these two gases combine to form a totally different substance in the liquid state. Can you help me out here?

That is the whole thing about rearranging atoms - the new substances ALWAYS have new properties compared to the original substances. In this case with new molecules there is a ton of hydrogen bonding that pulls the molecules into a liquid state at moderate temps. No such bonding in the original gases since there is no unequal sharing of electrons. In the water molecule, oxygen hogs the electrons which creates + and - charges across the molecule. And this creates H-bonding between water molecules.

Lou Harnisch

Dear Will,

If you fill a balloon with H2 and pop it in the atmosphere with a cold needle, nothing much happens (except the balloon pops). However, if you pop it with a hot needle, you get a loud "bang" as the highly exothermic reaction

H2 + O2 ---> H2O

occurs. This reaction is so slow at room temperature that it does not happen measurably when you just mix the gases together. However, add a little extra energy and.... you have the Hindenberg (which was filled with hydrogen gas).

It is hard to go into much more detail without knowing whether your students are K-5, 6-8 or 9-12 students. But the short answer is, it happens when the H2 and O2 are combined in the presence of a little applied heat.

Dr. Topper

Hydrogen burns in the presence of oxygen. The combustion product is water vapor.

To get liquid water you must cool it below the dew point.

Greg Bradburn

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