Differences between HHO and H2O

Question

I'm not an expert. In simple words how do they differ HHO and H2O molecules?

Answer 1

$\ce{H_{2}O}$ is the water molecule, two hydrogen atoms attached to a central oxygen atom, $\mathrm{C}_{2v}$ symmetry, thermodynamically minimal structure of these atoms, Adam's ale, etc.

HHO is a poorly defined term often bandied around by 'water powered car'... enthusiasts. I'm not sure that it's supposed to represent a molecule so much as a state of hydrogen and oxygen that conventional chemistry has no concept of.

• Here's a post on skeptics.SE about it
• And here's an acerbic article on rationalwiki that mentions 'HHO'

I think we're supposed to believe that it's a gas of hydrogen and hydroxyl radicals, or of atomic hydrogen and oxygen, or protons and hydroxide ions, or something, that is metastable at room temperature and that also happens to violate the first law of thermodynamics when produced and combusted. Why this glaringly obvious anomaly in quantum electrodynamics and thermodynamics has never been observed anywhere in nature before is anyone's guess (probably part of the conspiracy).

These guys should write up a few papers, get published in Nature, collect the Nobel chemistry, physics and peace prizes...

Answer 2

There is no molecule in existence with the structure H-H-O, for the simple reason that hydrogen possesses only one orbital and is therefore chemically incapable of forming more than one bond or maintaining more than two electrons in its orbit. Therefore, the formula $\ce{HHO}$ is either a very idiosyncratic way of denoting a molecule of water (normally written $\ce{H2O}$ and occasionally $\ce{HOH}$, in order to emphasize its structure, i.e., H-O-H), or it refers to oxyhydrogen, which isn't actually a molecule at all, but rather a mixture of hydrogen and oxygen gases (the molecules $\ce{H2}$ and $\ce{O2}$, respectively) used as a fuel.