# Combining H2 with 0

1. Oct 8, 2008

Hello All,
My question is;
If you have seperated H2 and O in gaseous form, then combine them at atmos press, what happens?
If combined in the pressence of a heat source what happens?
Randy

2. Oct 8, 2008

### Staff: Mentor

Welcome to PF. When you combine hydrogen and oxygen, that's combustion. They burn and the waste product is water. Though the activation energy isn't too high, it does exist, so there must be a heat source present to make it happen. Not all combustion reactions require a heat source (above ambient), though. Rusting metal is basically a very slow combustion reaction.

3. Oct 9, 2008

### Staff: Mentor

No such thing as free O, oxygen is diatomic, just like hydrogen - so it is O2.

4. Oct 9, 2008

### JGK

this was an experiment they showed me back in highschool.

A clean paint can was used:

2 holes were cut, one into the base and one into the lid. Hydrogen from a hydrogen generator was piped in via the base until the can was considered full (the H2 supply was shut-off then removed). the gas emerging from the hole in the lid was then ignited.

When the ratio of H2 to O2 reaches 2:1 there was a rather large explosion and the teacher spent the remainder of the lesson retrieving the paint can lid from the ceiling tile it was embedded in.

If you wish to do this experiment, you will need to be vary careful in order to avoid the inevitable lawsuits, accusations of terrorism etc., which will arise from any mishaps.

5. Oct 9, 2008

So i make the assumption that, (2)H2 + 02 ~> (2)H2O + ? + heat.
Also, H2 + O2 at atmos press does not spontaneously combust, an ignition source is required.
And a question, When comparisons are made between gasoline and H2 there is a ratio of one gallon of gas is equal to one litre of H2 in energy, is the litre gaseous or liquid?
PS thanks for the welcome!

6. Oct 9, 2008

### Staff: Mentor

For sure not gaseous.

Somehow I find this comparison hard to believe, but that's just a gut feeling.

7. Oct 9, 2008

8. Oct 9, 2008

### Staff: Mentor

Wikipedia has combustion energies: http://en.wikipedia.org/wiki/Heat_of_combustion

Hydrogen's combustion enery per unit of mass is a little less than 4x that of gasoline. So that's probably where the '1 gallon of gas = 1 L of H2' came from....of course, whoever made that comparison did not consider that liquid H2 has a specific gravity of .07...

9. Oct 10, 2008

### Staff: Mentor

More or less that's what I expected, I was just too lazy to dig into the real numbers. Thank you for checking