Basic Chemistry Question: H2 + O2 = ?

Two questions on H2 + O2:

a) Does lightning ever take H2 + O2 and make H20? I do not believe so, but I was just want confirmation from someone in the know. And, if it is possible, then the addition of energy can actually break bonds (H2O hydrolysis) AND make bonds?

b) How is H2O2 (hydrogen peroxide) made, and why isn’t the earth covered in it? We should be H2O2 based, and not H2O based organisms!

Science…very puzzling.

  • Jinx

The canonical formula for hydrogen combustion is:

2H[sub]2[/sub] + O[sub]2[/sub] → 2H[sub]2[/sub]O + FIRE!!!

In other words, two hydrogen gas molecules combine with one oxygen gas molecule to produce two water molecules, and this reaction is exothermic (it produces heat.)

There isn’t a whole lot of elemental hydrogen in the atmosphere, because it combines with oxygen fairly readily. Lightning seems as good a source of heat as anything for it to happen, but most water is probably produced by other means. (I don’t know what they are, though.)

As for hydrogen peroxide, you are making it right now. H[sub]2[/sub]O[sub]2[/sub] is a common byproduct of metabolic processes in all animals. There are further enzyme processes which lop off the extra O and make water and oxygen.

Peroxide is massively reactive and will reduce to water and oxygen.

a) has been answered, but I should add that you don’t necessarily need a heat source. If the idiot working next to you adds hydrogen to a flask containing air and Pd/C, you also get a fireball :smack:

b) Hydrogen peroxide is made industrially on a large scale by reducing a quinone with hydrogen, which is moved to a separate reactor, where the hydroquinone reduces oxygen. Then I think you have to extract out the quinone and distill off the peroxide or something. Anyway, I remember the wikipedia article having a nice explanation last time I checked, so I recommend that if you’re interested.

ETA it’s an anthraquinone

What’s Pd/C?


You don’t need “heat” to start a reaction, you need to get enough of the molecules on the left side of the equation to have enough energy to react with each other. This can be achieved by adding energy to them (heat, lighting, light are good sources) or by lowering how much energy is needed (done by a catalyst, like that Pd/C).

Of the various substances you have mentioned in your question (H[sub]2[/sub], O[sub]2[/sub], H[sub]2[/sub]O, and H[sub]2[/sub]O[sub]2[/sub]), the most stable form at room temperature and pressure is H[sub]2[/sub]O (water).

All chemical reactions involve the breaking and reforming of chemical bonds. The energy it takes to break the initial bonds and get a reaction going is referred to as activation energy. In the case of an endothermic reaction (such as the hydrolysis of water), energy has to be continuously added to keep the reaction going. In the case of an exothermic reaction (such as the combustion reaction of hydrogen with oxygen), you just need enough activation energy to get the reaction going, and the reaction will produce enough heat to keep the reaction going until one of the reactants is exhausted. This initial activation energy could be a spark or the flame from a match.

The presence of a catalyst such as platinum or palladium acts to lower the required activation energy necessary to get the reaction going, perhaps to the point that the reaction can proceed at room temperature, with no initial spark or flame needed.

Not once you understand what’s going on.

Please understand that I’m not intending to be snarky at all here, but have you ever considered taking an introductory chemistry course?

My father used to do this with his Science classes - he’d pour some washing up liquid into a pupil’s palm and then have them hold it flat while he’d inject small amounts of H2 and O2 gas (twice as much of the former obviously) under the soap so as to create a bubble, which he’d then light with a long taper. It explodes with an almighty bang, but since the palm is flat, most of the force is direct up, away from the hand. It feels (having been a subject myself) like your hand has been slapped quite hard, but sounds like it has been blown right off!! Very impressive…

There is enough energy in lightning to atomize everything. It wouldn’t break water into H2 and O2 though, it would break it into H and O. Of course they are likely ionized at some point. They will then recombine in many ways. Ozone (O3) is the smell of a lightning storm, but water is probably also made.

Can I ask a question about that formula?

Why isn’t it:

2H[sub]2[/sub] + O[sub]2[/sub] + FIRE → 2H[sub]2[/sub]O (+ heat, maybe)

To my way of thinking, if you have the hydrogen and oxygen, they won’t react without the addition of the fire, and once the reaction is done, you get water (plus heat, if the reaction produces more energy than it consumes).

I’m sure my understanding of this is what’s in error, but could someone help me out and show me where my reasoning is flawed?

I think the fire friedo was talking about is the heat produced when hydrogen combusts in oxygen, and you do get a nice bang if you ignite hydrogen. You are talking about activation energy, the little spark needed to get the reactants over the “energy hump” and start reacting.

Indeed – it’s how we got to the moon.


Ah, I see now. Thanks for clearing that up! I figured there must have been something I wasn’t getting.

Massively reactive, of course, equates to massively toxic - particularly if you have it running around inside your cell. Peroxide’s reduction will strip off electrons and blow molecular bonds apart in the process. This ‘oxidative stress’ is thought to be one of the contributing factors in the aging process. Virtually all organisms have enzymes to directly reduce peroxide and other similarly reactive oxidizing species; these are some of the most efficient enzymes known.

And if you want to the body’s decomposition of hydrogen peroxide in an impressive and gross way, get a few liters of pig blood from a butcher, then dump an aqueous solution of hydrogen peroxide into it. Massive foaming tower of blood. :eek: