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Would the lesser gravity of the moon, the microgravity of the space station and lack of Earth's atmosphere make a difference in atomic or chemical reactions?

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  • $\begingroup$ as both the answers you got are reasonable, the one of the secondary effect of gravity on pressure which surely has an effect in chemical reactions, and the other on basic interactive chemistry treating gravity on par with the other forces, you must not mix the space station environment, which has earth atmosphere pressure with lack of earth's atmosphere. you should edit $\endgroup$
    – anna v
    Dec 16 '17 at 7:00
  • $\begingroup$ As far fundamental laws are concerned, or about the role of tge weight of particles , I have nothing to say. But conducting a reaction is more. It requires most often convection, layers and bubbles might form, etc. All these affect chemistry, in a practical sense. $\endgroup$
    – Alchimista
    Dec 16 '17 at 11:05
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Any chemistry that relies on convection to mix the constituents is clearly affected by zero gravity.

A candle flame will self-extinguish; see https://www.youtube.com/watch?v=9zdD7lfB0Fs

When the Apollo-13 astronauts wanted to warm the contents of their liquid oxygen tank, they first needed to turn on the electrically driven stirring motors. Oops...

Residents on the ISS need fans running all the time to remove exhaled air from around them as they sleep.

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Yes. Pressure matters. Pressure on Earth is often a result of gravity.

Water boils at room temperature in a vacuum. Diamond is stable deep in the earth. At the surface, it (very slowly) turns to graphite.

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Just to be contrary to @mmesser314's answer, No. That is, pressure effects aside, see, e.g., http://hyperphysics.phy-astr.gsu.edu/hbase/Forces/couple.html#c5 where it shows that the gravitational force between an electron and proton is some $10^{39}$ times weaker than the electromagnetic force between them. And that's a real small perturbation by anybody's standards (i.e., a little technically, solutions to any kind of pde's involving Hamiltionians wouldn't be measurably affected).

For example, the Earth's mass is $\sim6\times10^{24}\mbox{kg}$, so one part in $10^{39}$ is like adding $\sim10^{-11}\mbox{gm}$ to the Earth, which is about the mass of a single E.Coli bacterium (as per https://hypertextbook.com/facts/2003/LouisSiu.shtml). So you might somewhat loosely compare the effect of gravity on chemical reactions to the effect of a single E.Coli bacterium on the Moon's orbit around the Earth.

And for a kind of converse example, if the electromagnetic force were as weak as gravity, then the (first Bohr) radius of hydrogen atom (about $5.3\times10^{-11}\mbox{m}$) would instead be roughly the distance from Earth to the nearest star (besides the Sun).

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  • $\begingroup$ +1. But there are other ways where gravity matters in ways that are kind-of sort-of chemical. Mixed oil and water will separate into two layers because of gravity. Stalactites form vertical columns because of gravity. Meteors go really fast and burn up when they hit the atmosphere because of gravity. Streams erode mountains because of gravity. Yeah, this is all cheating. Just be be contrary :) $\endgroup$
    – mmesser314
    Dec 17 '17 at 2:45
  • $\begingroup$ Thanks @mmesser314 , and +1 to you, too. Sure, I completely agree gravity matters. When I began by saying "Just to be contrary", that was kind of tongue-in-cheek. That is, I wasn't disagreeing with you. Rather, I was just pointing out the additional view, which (at)annav nicely described in her comment to the op's question. $\endgroup$
    – user89220
    Dec 17 '17 at 5:39

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