[houston_Euler]

Can you point to some evidence for the claim that "a molecule of water is lighter than the oxygen and two hydrogen atoms that went into making it?"

I could understand the atoms sharing electrons, but just want to make sure I'm understanding you correctly, because you said it's unexplained.

[marcosdumay]

You mean experimental evidence? I don't think our mass measurements are that precise.

Just to be clear, that statement is very well accepted physics, and we have plenty of evidence of bounding energy changing the mass of things on the more energetic reactions (the nuclear ones). It would be incredibly surprising (in "redo all of physics" surprising) if it didn't hold for chemical reactions too, but I don't think anybody has evidence.

[Keyframe]

You mean experimental evidence? I don't think our mass measurements are that precise.

You don't need to weigh individual atoms or molecules to take measurement!

Just to be clear, that statement is very well accepted physics, and we have plenty of evidence of bounding energy changing the mass of things on the more energetic reactions (the nuclear ones). It would be incredibly surprising (in "redo all of physics" surprising) if it didn't hold for chemical reactions too, but I don't think anybody has evidence.

Not sure I follow your direction here. Seems to be a conflation of three separate things, not necessarily compatible with each other. In classical physics mass and charge (of a particle) are different properties. One defines how particle behaves in response to forces, the other how it interacts with em fields. That's one. The other, if we go into relativistic physics, there's mass-energy equivalence (as stated by einstein)... however, charge itself isn't a form of energy, BUT charged particles can have energy associated with their electric fields that would contribute, in a sense, to the overall mass-energy of a system (which is usually ignored unless we're talking sub-atomic particles or high-energy physics). That's two. And then there's binding (not bounding) energy which represents the amount of energy required to split a system of particles into its non-interacting components (such as, in context of nuclear physics, splitting a nucleus into protons and neutrons).. or you've meant electron binding energy which represents amount of energy needed to remove an electron from an atom.. that'd be a third.

[fsh]

The mass ratios of charged particles, such as atomic and molecular ions, can be measured incredibly accurately in Penning traps. Some of the most accurate comparisons are between the mass-3 ions ³He⁺, HD⁺, T⁺, and H₃⁺. Of these, only H₃⁺ has long-lived excited states, and the different excitation energies are clearly resolved in the mass comparisons [1]. The binding energies are much larger and have to be taken into account in the comparisons.

[1] https://doi.org/10.1103/PhysRevLett.120.143002

[XorNot]

Well yes but the energy scale involved is tiny. We notice these things with nuclear reactions because the energies are much higher.

The chemical energy in the electron orbitals is far lower by comparison (infrared as opposed to gamma radiation).

[JumpCrisscross]

> Can you point to some evidence for the claim that "a molecule of water is lighter than the oxygen and two hydrogen atoms that went into making it?

Not OP, but burning hydrogen in oxygen is exothermic. It makes intuitive sense that the energy from that reaction no longer contributes to the mass of its products.

[naasking]

https://en.wikipedia.org/wiki/Binding_energy#Mass_change

[jdkee]

Per our new electronic friend:

" The weight of a molecule of water (H2O) is the sum of the weights of the two hydrogen atoms and one oxygen atom that compose it. Here are the atomic weights of these elements:

Hydrogen (H): Approximately 1 atomic mass unit (amu) Oxygen (O): Approximately 16 amu So for a molecule of water:

2 Hydrogen atoms: 2 * 1 amu = 2 amu 1 Oxygen atom: 16 amu Adding these together gives a total of 18 amu for a molecule of water.

This means that a molecule of water has the same weight as the sum of the weights of the two hydrogen atoms and one oxygen atom that compose it, because the molecule is simply a combination of these atoms. There's no loss or gain in weight when the atoms combine to form the molecule.

However, this does not take into account the minor decrease in mass that occurs during the formation of a water molecule due to the conversion of some mass into binding energy according to Einstein's equation E=mc^2. This decrease is incredibly small and generally not considered in standard atomic weight calculations, but it does technically make the water molecule ever so slightly lighter than the sum of its constituent atoms."

[eigenket]

I would say this phrase

> the minor decrease in mass that occurs during the formation of a water molecule due to the conversion of some mass into binding energy according to Einstein's equation E=mc^2

Is highly imprecise at best, and misleading at worst.

It is true that the mass of the water molecule is slightly less than that of the oxygen and hydrogen atoms combined. It is not true that this excess mass is converted into "binding energy", binding energy is negative in stable molecules. That is the binding energy measures how much energy you would have to add to break up the molecule, or conversely, how much energy is lost (as heat/light/whatever) to the environment when the molecule is formed.

The mass is lower because it has been converted into heat in the environment, not because it has been converted into binding energy.

---------------

I would call this an instance of the language model producing convincing sounding nonsense (something that they do quite often when asked about technical stuff).

[Sakos]

Okay, somebody explain these downvotes, because afaik none of these statements in this comment or the other downvoted comments about the mass of water are incorrect. Somebody make it make sense.

[tsimionescu]

I believe this one is downvoted for quoting Chat GPT. The other one is downvoted not so much for the claim about water molecule mass, but because of the combative tone and feeling that it is challenging established physics in a somewhat shallow way, most likely.

[jiggawatts]

It cracks me up that my comment is seen as "challenging established physics" (and being downvoted into oblivion) when literally everything I stated is established physics.

I really don't see what's controversial about what I've said that's riled up people so much...

[rcxdude]

It is factually incorrect in the assertion that the standard model can't explain the reduction in mass (special relativity and quantum mechanics work fine together. It's general relativity that is the problem). In fact mass-energy equivalence is a pretty core part of quantum mechanics.

[jiggawatts]

> In fact mass-energy equivalence is a pretty core part of quantum mechanics.

It may be stated as such, and added in to equations as an external piece of knowledge from relativity, but this is cheating a bit.

Essentially, when we state that H2O has less mass than H+H+O, what we actually mean is that H2O bends spacetime a little bit less than the three atoms individually that made it up. There's no accepted variant of QM or the Standard Model that explains this. The dynamics of spacetime curvature rearranging as the photon is emitted as the hydrogen atoms burn is not explained by modern science. This is fundamentally the "QM is incompatible with GR" issue.

My point was that it isn't just near black holes that a GR-compatible microscopic theory is relevant.

It's relevant even in the flame of a candle. It's a small effect, but it's there. The inconsistency in the theories occurs at all scales.