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Comment by PeterisP | Hacker News Reader

Well, sure, but energy=mass; just as an atom's mass is not equal to the sum of the protons, neutrons and electrons masses but depends also on their binding energy, in the same manner, a compound with highly energetic chemical bounds has a (very, very slightly) different inertia and gravity than the separate components. The difference of this effect between atomic and chemical bounds [spelling? English isn't my main language] is quantitative, not qualitative; chemical bounds have much less energy, so the effect is much smaller, so for most purposes it can be considered as insignificantly small, but it's still there and not zero.

Any system that loses energy (e.g. releases an energetic photon - no matter if it's because of a nuclear or chemical reaction) also loses mass, though E=mc^2 means that losing reasonable amounts of energy mean losing very, very small amounts of mass.

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Thank you for the explanation, that makes perfect sense.

So... the energy content in wax is about 45MJ/kg. An 8 in ch taper candle weights about 40g. This means it contains about 1.8 MJ of energy.

Of that 40g about 20 nanograms turned into energy! That is about 0.5 parts per billion.

https://physics.stackexchange.com/questions/195696/do-chemic...

Seems the unanimous answer is 'yes', which surprised me. I considered that chemical bonds are actually changes in electromagnetic potential (i.e. similar to the leaves in a Leyden jar repelling, converting electrical potential to gravitational potential). With no change in mass, I expected that the relativity equation would zero.

That's the whole point - the inertial and gravitational mass of the system is proportional to the total energy of the system; changes in electromagnetic potential affect the energy within and thus also the mass as far as inertia or gravity is concerned. The same applies for electrostatic potential and gravitational potential. "Rest mass" is just a form of energy - after all, the rest mass of e.g. a block of lead consists mostly of the rest mass of protons and neutrons inside, but the rest mass of those protons and neutrons does not consist of the rest mass of their components, but mostly of the binding energy between their quarks - so the block of lead weighs as much as (and because of) the stored binding energy.

> bounds [spelling? English isn't my main language]

"Bonds" is the spelling. I don't normally correct spelling here, but you did ask.

>Any system that loses energy (e.g. releases an energetic photon - no matter if it's because of a nuclear or chemical reaction) also loses mass

Lol sorry my friend but this is just plain false. Photons can carry away energy in the form of momentum but they're massless. Remember, it's E^2 = (pc)^2 + (mc^2)^2. Nuclear reactions can involve the conversion of mass into energy because they involve the strong force, but that's not how chemical reactions work.

Think about it like this: you have two H atoms bump each other perfectly and come to rest, and in the process an electron gets excited to a higher energy state. Eventually it spontaneously pops back down, emitting a photon that escapes. The mass of the two H atoms is unchanged, but a photon took energy away. It carried away momentum, not mass.

"The mass of the two H atoms is unchanged" -> No, if an electron on an H atom is excited to a higher energy state, the mass of the atom increases (although with the relatively low energies involved, that mass increase is extremely tiny). The mass of nucleus isn't equal to the mass of neutrons and protons, the binding energy matters, and the mass of an atom isn't equal to the mass of the nucleus plus the mass of the electrons, the energy states matter.

Not an authoritative reference, but perhaps a sufficient explanation is here - https://physics.stackexchange.com/questions/149744/does-the-...

You ignored the part where the electron decays back to the lower energy state. The ending states are the exact same as the initial states, since the electron decays back to the lower (initial) state by emitting a photon. The photon carries away momentum, but the mass of the two particles is unchanged.

energy != mass; e=mc^2 declares there is a proportional relationship between energy and mass while the speed of light, c, squared is the constant of proportionality.

You can set c to 1 if you want, then energy == mass.

As a matter of fact this is pretty common in particle physics where all masses are given in electronvolts.

https://en.wikipedia.org/wiki/Geometrized_unit_system

"there is a proportional relationship between energy and mass" -> exactly. the mass of the system is strictly proportional to its total energy, and changes in the energy of a system will have a corresponding proportional effect on its mass.

If you split the system into two components and release X energy, then the two components will weigh X/c^2 less than the whole system did; if splitting the system consumed X energy, then the separate components will weigh X/c^2 more than the original thing.

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