Does one molecule of H2O weigh the same as 2 Hydrogen and 1 Oxygen?

[Jeff7]

Originally posted by: MrPickins

Originally posted by: LordMorpheus
Actually, because an H20 molecule has less energy than 2 hydrogen atoms and an oxygen atom, H2O will have very slightly LESS mass than the three atoms floating around independently.


Just saying.

As noted above though, the difference is so small as to be practically negligible.

Hence his use of the words "very slightly less mass."

I think it has to do with some kind of binding energy. Take two hydrogen, bond with oxygen. What happens? Energy is released.
e = mc²
m = e/c²

The mass lost should equal the energy released divided by the speed of light squared. In other words, a really really tiny amount of mass. But it does happen.
You also see this in nuclear reactions. If you fuse two hydrogen nuclei into 1 helium nucleus, that helium nucleus will have slightly less mass than the two hydrogens put together, due to the release of energy during the fusion process.
This occurs up to iron - after that point, fusing nuclei absorbs energy; breaking apart the nuclei is what releases energy then. That's why fusion is done on light elements, and fission is done on heavy elements, if the objective is to obtain a release of energy.

 

[DrPizza]

Originally posted by: Demon-Xanth

Originally posted by: DrPizza

"hydrogen has no weight because it's lighter than air"


Lighter means it weighs less, not that it has no weight. Does a dead whale have no weight because it floats in water?

Also, for the "negligible" amount of mass that's lost: it's pretty simple to calculate:
E=mc² Look up the energy for the reaction of hydrogen with water.

Hence my comment of "fly on a cruise ship". Does the fly increase the mass? Yes. Is it measurable? Conceivably. Does anyone care? No.

By putting the word "negligible" in quotation marks like that, I suppose I was a little ambiguous to what I meant. I didn't mean that it was a significant amount of mass. The speed of light squared is a pretty big number! Of course dividing by it is going to result in an insignificant amount of mass that's lost; practically zero mass. My point was that too many people don't believe that mass is lost and converted to energy during chemical reactions. Too often, people only believe that E=mc² only applies to nuclear reactions where atoms are split or fused. They don't realize that when they turn on the burner on their stove, E=mc² applies there just as accurately. This is because it's neglected to be taught; hence my "negligible."

 

[Rubycon]

Originally posted by: Demon-Xanth
Hence my comment of "fly on a cruise ship". Does the fly increase the mass? Yes. Is it measurable? Conceivably. Does anyone care? No.

I care. Flies are disgusting!

 

[SSSnail]

No stupid, H2O is water therefore it's wet. Now, we all know wet things are heavier than dry things.