Sorry, I don’t see how this helps the OP. It sounds like you’re talking about looking at the behavior and any transitions over a very long time rather than relying on the ergodic hypothesis and stat mech assumptions based on large N. OK, so now you’ve calculated what you consider the entropy. I don’t get how this allows the OP to classify the atom as a bulk solid, liquid, or gas when it’s a lone aqueous atom.

> Like it becomes free Na and Cl just floating around in water right?

They aren't free, they're solvated—that is, they're stabilized through interactions with the surrounding solvent. This is why they don't immediately bond, so we can't remove this crucial aspect.

> One bit of nitpick. Entropy is still very well defined even at the atomic level. There's many different types of entropy, but they all are related to the same underlying concept.

Isn't it clear from the context that I'm referring to the thermodynamic entropy as applied to ensembles of molecules to determine the equilibrium bulk state?

>Plasma seems intuitive because you are stripping pieces of the atom away, but what about the three basic phases?

Whether a simple material is a solid, liquid, or gas at equilibrium depends on which phase has the lowest Gibbs free energy at that temperature, pressure, and other conditions.

Nature prefers both strong bonding and high entropy, and the Gibbs free energy incorporates both as a tradeoff: It's the enthalpy minus the temperature multiplied by the entropy. This is why the higher-entropy phase always wins at higher temperatures: solid to liquid to gas. Visualization.

Thermodynamic entropy in this context is an ensemble property that isn't well defined for a single atom, so it doesn't make sense to talk about a single atom having a certain equilibrium phase.

Energy minimization is a consequence of entropy maximization, as I derive here.

Broadly, when things fall into a lower energy minimum, they heat the rest of the Universe, which increases its entropy. Nature loves this.

> What decides which thing gets to have low energy?

The configuration with higher entropy. It has more ways to appear, so we see it more often. That’s the Second Law, in essence.

At equilibrium, there’s no difference in any intensive parameter: temperature, pressure, stress, chemical potential, surface tension, electric field, you name it.

> Your answer seems to imply that if the system was spinning, you would call it higher temperature

That would be a misreading, because the context of the answer is a question about translational motion. More generally, the bulk motion is typically subtracted before we do thermodynamics. If you don’t see that stated in definitions of temperature, it’s because it’s already been implicitly assumed.

> As a side note, you would observe blackbody radiation that was red- or blue-shifted depending on your motion that could make the gas appear warmer or cooler.

A hotter or colder body's blackbody radiation isn't simply shifted by a set amount, so this isn't true. You'd identify the same temperature with some overlaid bulk motion. I apologize; my statements were incorrect.

No; the kinetic energy corresponding to the temperature is measured relative to the center of mass. A cold body moving fast doesn't appear hot, as the relative undirected motion of the particles is unchanged. (However, two cold bodies colliding inelastically would get hotter, of course.)

The origin is freezing point depression. Broadly, salty water - and the water can come from skin moisture alone - has a lower water concentration (<100% water) than pure ice (100% water), so water tends to move to the area of lower concentration. (This is equivalent to the equilibrium melting point going down.) But this movement requires melting, which absorbs substantial energy corresponding to the latent heat and makes the system and the surroundings much colder. This translates into much more severe freezing of tissue than with ice alone. Make sense?

I was just looking for “It’s dimmer.” That’s what provides the energy that’s absorbed in the medium, not any change in frequency.

Well, what's different about monochromatic light that's passed through a filter?

The frequency is the same everywhere. (The easiest way to see this may be to note that the electric and magnetic fields must be in sync everywhere, including the interfaces.)

The medium plays a part in the momentum transfer, yes.

The net force on a spherical body isn't zero for a single beam because the beam changes shape moving through it, so the refractive details are different on either side.

But for two counterpropagating beams, which is what I used, the left–right forces do balance out, leaving an internal tensile load that stretches a compliant medium. You don't notice this in everyday situations with macroscale objects because they're stiff and the light is weak.

No one thing is decelerating or accelerating. The photon–matter interaction propagates slower than c.

See the discussion here and the links within, for example.

As I recall, the energy is split between absorption, reflection, and refraction. The frequency of the light wave stays the same; its speed changes. Remember that we’re talking about light interacting with matter, rather than lone photons in a vacuum.

Thank you! I always forget to escape the parentheses on Reddit.

I did a PhD involving this. Yes, light passing from one medium to another gives the interface a momentum kick. (Edit: example video, not mine.)

Beautifully described!

>absolute zero is impossible because you lower a temperature, you need something below that temperature.

Fortunately, this isn't the reason, because it's not true. If you've ever been in 35°C weather or hotter, you lowered your own temperature without there being anything below that temperature. You probably didn't even think about it!

As a side point, it's not. Such counters click down from 0 to the maximum count since they can't represent a negative. Temperature is different—arguably, the more fundamental parameter is the reciprocal 1/T, which is positive in most familiar systems but can in some circumstances swing below zero. This implies (very weirdly) that the temperature shoots up to ∞ and then to -∞. Again, it takes special effort to construct such a system; it won't occur around the house.

My note addresses the comment only, not any aspect of your character. Of course insults have no place in a technical discussion.

> For example, strain in metals is due to the crystal structure "realigning" itself, one atom at a time. Doing so fills atomic-scale voids and fixes other defects in the structure. Eventually, you run out of such defects, and the stress is instead applied to the crystal bonds themselves.

[Edited to assume good faith.] This is so very wrong. I suppose you're just making things up or using an AI-generated answer writing without peer-reviewed technical references; the answer also resembles AI-generated answers that are designed to be confident but not designed to be correct.

Elastic strain arises from bonds stretching and recoverable defect movement. Plastic strain arises from unrecoverable defect movement, which itself creates more defects, not fewer. Voids ultimately form and coalesce; they don't disappear. The stress is always applied to the crystal bonds.

>I was talking to a coworker and he said that the hot air in the chamber was cooling the part because it was flowing.

This can be true only for a part that's perspiring.

I’m referring to a monolayer.

> to the naked eye they would most likely appear off-white.

Single cells would appear clear. Agglomerations of many, many cells would appear off-white for the same reason that milk or snow appears off-white: indiscriminate scattering of white light.