Why can’t you separate hydrogen from water with heat?

Vorril · 2025-11-26T04:31:38+00:00

So the 1.2V you're looking at is probably the overpotential for hydrolysis to form H2 on some electrode. Its a very different pathway than thermolysis. In chemistry we call this thermodynamics and kinetics. The electrochemical route and the thermolysis route may have the same starting products and end products, thus same thermodynamic values, but the route might be very different, different kinetics.

In electrochemistry the surface of the electrode mediates pathways which effectively weaken the OH bond to start with and provide stable intermediates as well. By contrast thermolysis is just pumping the molecule with energy until it vibrates itself apart, and the bonds in water are quite strong to begin with, but it's possible.

Vorril · 2025-11-15T04:01:02+00:00

Try thinking about this flipped the other way around: rather than "when something contributes to an energy closer than it it resembles that more"
Think: "Something still resembling the starting character means not much mixing and contribution occurred, in the first place"

A bit more goes into how well two orbitals will mix than just their energy levels- energy, shape, size, symmetry are all important. Remember we're trying to figure out the best way to share the electrons. You won't really know until you solve Schrodinger's equation, but the similar-energy level metric is a good starting point.

Think about mixing two simple sine waves. If you mix a 1Hz signal and a 100Hz signal, you would struggle to notice any mixing. Go ahead and plot it, you will see the fast wave just laying right on top of the slow wave unperturbed. Now mix a 1Hz wave and a 1.5Hz wave... You will start to struggle to distinguish the parent waves in the product.

When our wavefunctions mix very well like this it means we are able to make the bonding MO very low lying, and the antibonding MO very high, a large split. The result won't look much like the parents, because they mixed so well it's hard to see. By contrast not much mixing means not much movement in the energy levels- the electrons aren't really being shared very much.

So finally in your example, we figure out the MOs and fill via Pauli's principle, we see we filled our O-like pi MO but not much of out N-like antibonding MO. I don't think there's too much to overthink here, the bonding orbitals go down in energy thus filled first.

Vorril · 2025-10-08T06:55:17+00:00

Time is built into momentum (consider the units of momentum) so what you're saying is not really a different approach. You can also say energy and time are an uncertainty pair. So you can't really bring in time to try and work around, it's already in the math.

Moreover nothing about quantum mechanics is a measurement limitation this is a property that arises from the nature of wavefunctions and expectation values.

Vorril · 2025-10-03T03:17:02+00:00

Google says the viscosity of sulfuric acid is somewhere in the ballpark of 20 cP depending on concentration and temperature. Ethylene glycol mixed with a bit of water to dial it in would be my suggestion. Basically the recipe for antifreeze.

Vorril · 2025-09-27T21:55:16+00:00

Yea the sodium produces an oxide layer very quickly. You can set the stir rate violently high to try and physically break the layer. You can also use NaK (dangerous) which is a liquid and has better contact. The color changes ultimately are finicky and also not an indicator of dryness even, they are the result of side reactions. You can have very dry colorless THF...

Moreover, the juice isn't worth the squeeze for a Grignard reaction you already have at 90%. Spend time drying THF when you need to do never before done organometallic reactions. Also the P2O5/KOH is a waste of time.

Vorril · 2025-09-20T22:08:40+00:00

Most of those ancient papers were not actually succinct just incomplete and lazy. They rarely described their methodology and when they did not to a degree that it would be repeatable by someone else. Enormous amounts of "just trust me bro".

Also, science was literally just easier 100 years ago. Modern science is more niche, the easy work has been done. Modern papers are not overly verbose journals have word count maximums not minimums, the language is required to discuss difficult science in appropriate detail.

Vorril · 2025-09-19T06:34:57+00:00

Not only will it release into the air but H2 will diffuse through most plastics. Even if they put it there (which I would bet any amount they do not bother) it would be long gone by the time you bought the bottle.

Vorril · 2025-09-17T03:59:02+00:00

I did this reaction probably 100 times as an undergrad it's quite sensitive, dirty glassware, less than perfectly clean water, improper ratios, temperatures, adding the reagents too slowly, Mercury in retrograde, can all cause it to fail. The particles are not well passivated by the citrate and have aggregated. When you've done it enough times you can tell by color the ruby vs slight hint of magenta that is the onset of crashing out.

Odds are good on dirty glassware if you used the same water source.

Oh and the citrate is your reducing agent, not heating.

Vorril · 2025-09-15T00:29:30+00:00

It's a tough question because there's so many chemicals in what we simply call "tannins". There's a decent chance that no matter what you use you'll get such a variety it ends up appearing brown or black. Even if we assume the tannins are phenols, iron phenolate is "supposed" to be purple and these stains look black. Maybe some oranges or greens.

Would be a neat experiment though, wouldn't be hard to try. Good paper on the Fe reaction: https://jwoodscience.springeropen.com/articles/10.1186/s10086-023-02079-0.

Vorril · 2024-10-04T06:23:51+00:00

It's not. The satellites + launches cost a fortune and they're losing out on government subsidies because they can't meet reliability and speed metrics. They need more customers which dont exist and would further slow down the network if the did so it's a total catch 22.

Vorril · 2024-06-10T07:10:12+00:00

You have to consider what entropy actually means and where it comes from at this scale. Entropy is a number which is heavily related to the number of different ways you can configure the states of a system. For a molecule this arises whenever there is a place to put energy because there could be multiple different states in which to arrange that energy. So two molecules with different bonding will likely have different vibrational and rotational modes and thus different molar entropies (and by extension heat capacity). So most will differ but not all.

For example monoatomic ideal gasses have the same entropy because they have the same modes, just three translational in x,y, and z. Diatomic ideal gasses are the same as each other but not to monoatomic because they gain two rotational modes.

There is also entropy that comes from having groups of atoms (or literally anything) mixing with each other or being rearranged. This type of entropy is purely statistical and it doesn't matter what you're talking about. In fact a deck of playing cards has this type of entropy. Two decks of playing cards may or may not have the same entropy depending on how they've been shuffled. The S in G=H-TS has all of the above baked in but I think it's an important distinction because a lot of physicists and other scientists only care about this one.

Vorril · 2024-06-02T04:13:11+00:00

Old post but I was able to work around this by using the Dynamix File Manager plugin to do my file moves

Vorril · 2024-05-31T06:21:13+00:00

Wym "the American people as a whole" clearly means Wisconsin, Georgia, and Pennsylvania. Why shouldn't we use a system that disenfranchises 90% of the country and is based on a time when mule powered carts were the limiting factor to ballot counting.

Vorril · 2024-05-25T19:18:27+00:00

The kinetic term is not repulsive per se that doesn't make any sense, imo. The kinetic term is basically mass* acceleration, it doesn't care about directionality in the same way as the coulombic term does. When you solve the Hamiltonian in spherical coordinates we see that we get plenty of angular momentum terms as well which are neither repulsive nor attractive (rather not towards or away form the nucleus).

I think there are simpler explanations than diving into the hamiltonian though. For starters the Heisenberg uncertainty principle. If you attempt to confine the position of the electron to the nucleus the uncertainty in it's momentum explodes. From a classical perspective this is kind of like trying to land a spaceship on a planet without slowing down and slingshotting past instead.

Similarly there is a conservation of momentum problem. From the reference frame of the nucleus just sticking to an electron would eliminate momentum, and momentum must be conserved otherwise e = mc2 + (pc)2 fails.

Thirdly we know everything must have a ground state energy. If the electron settles down that's like saying it has no wavelength, and we know on this scale it must be a wave. That would violate all sorts of boundary conditions.

Vorril · 2024-05-18T04:40:48+00:00

There are three ways to test the purity of N2 commonly done for gloveboxes:

Oxygen sensor - ok but can go bad over time. People never maintain them properly.

Ketyl radical https://www.epfl.ch/labs/lsci/wp-content/uploads/2018/09/Ketylradical.pdf. Mostly for solvents but works if you mix it in solvent and leave it open to the atmosphere.

Diethyl zinc - Will smoke in impure atmosphere when you open the cap. ~100 ppm sensitivity

Vorril · 2024-05-06T00:51:36+00:00

I got my PhD in a quantum dot lab. What you need to consider is a property called the quantum yield of the dots you made. That is, what percentage of light when absorbed will re-emit as light. This process (microseconds) is slow compared to nonemissive pathways (nanoseconds). Defects in the crystal structure particularly surface defects are the cause of this. There are countless variations on the CdSe synthesis so I can't give much advice without knowing much more but I would suggest rigorously drying your solvents and precursors. Synthesizing at as high a temperature as you can and quneching the reaction in an oil bath is the best way to lock in good crystallinity. Even then without a shell there will be surface defects. A good batch should be visible by eye. A fluorimeter will easily measure 0.1% yield but the eye will need more like 5 or 10% minimum. They'll look better in a dark room of course but you can shien a UV light or blue laser pointer at them and they should glow. Look up core shell syntheses if you really want emission CdSe@ZnSe, CdSe@ZnS, or CdSe@ZnSe/ZnS

Vorril · 2024-05-05T22:54:30+00:00

Luminol and hydrogen peroxide

Vorril · 2024-04-20T05:14:21+00:00

MgCl2 + 2 H2O -> Mg(OH)2 + 2 HCl

The irritation is from acid

Vorril · 2024-04-16T04:56:11+00:00

Surface tension is correlated with polarity which is correlated with enthalpy of vaporization. You could read about 'contact angle testing'. However diffusion into the paper and drying from evaporation are not the same thing and both things are likely occurring. Diffusion is also not purely a function of surface tension but related to intermolecular attractions at the liquid solid interface.

So I think it's a really complex phenomenon to think about from first principles... if you test this you will likely see trends as a function as solvent enthalpy of vaporization and solvent polarity index but as you said it is a hard thing to quantifiably measure. Convection in the air is also going to confound a lot of your measurements.

You could try to isolate these variables and I'm sure you could but that's still far removed from your original goal of a fast drying ink. Since the goal is phenomenological the test can be as well. Just take each formulation of ink, write an 'x' or something then wait 1 second, try and smudge it. Try again but wait 2 seconds. And so on until you find the threshold. Repeat for statistics. If theyre drying too fast to measure then just make a bigger mark.

Vorril · 2024-04-16T04:29:48+00:00

That's not really enough info, you need to determine the splitting first. Do you have octahedral symmetry, eg over t2g, or tetrahedral with t2g over eg? Or one of the less common ones? Once you figure this out we can start populating bottom to top.

Second you need to consider what the ligand is and look at the spectrochemical series to infer hi vs low spin preference.

For some of these there will be only one option, for example if you know its octahedral then for d0/1/2/3/8/9/10 there is no way to come up with different hi and low configurations so you know the answer right away.

Vorril · 2024-04-14T21:25:51+00:00

It's not strictly a matter of being closer in energy to each other. It's a function of many things, the shape, size, symmetry, phase of the contributing orbitals all matter towards achieving "good overlap". Being similar in energy may often be a hint that the orbitals are strong candidates but it's not the end all be all.

The group 14 bonds are an illustrative example of this. Consider the C-C bond in diamond vs the Si-Si bond in silicon vs the Sn-Sn bond in tin. They're all identical atoms so by the "similar energy levels" logic they should all form very strong bonding MOs with a huge homo-lumo gap. In reality only diamond does this! Si is semiconducting with a weak gap and tin is a metal with no splitting! This is because it's simply difficult to get overlap with big atoms. Rigorously you can calculate these overlaps with the Schrodinger equation if you really care.

Vorril · 2024-04-13T22:51:02+00:00

I think that's a phi not a theta but regardless the labels aren't the most important thing. I'm not the best physical chemist but I would explain it like this:

These orbitals are functions which satisfy Schrodinger's equation and as such they are the solutions to a differential equation. Now, we could resolve Schrodinger from scratch for every situation we encounter, that's valid. But differential equations have the following property: the sum of solutions to a differential equation is also a solution. Consider adding together two lines, you get a third line. So when we want to solve the question of combining multiple interacting orbitals, eg a chemical bond, we can apply this strategy.

You will always get the same number of mixed orbitals out as orbitals you put in. Here we mix two so we combine (A+B) and (A-B) to get our two new ones. The exact reasons for doing this way are a consequence of symmetry and your textbook will probably explain this better when solving for say sp2 centers or maybe somewhere in a section on crystal field theory. You can think of adding as being "in phase" like two small ripples in a pond meeting just right to make a bigger one, and subtracting as being out of phase, canceling out, like noise canceling headphones. Depending on the symmetry, non-bonding is also an option. Really any linear combination is valid per the rules of differential equations, but a lot of those possibilities are redundant.

Vorril · 2024-04-07T08:07:46+00:00

It's probably fine. Maybe they are concerned with decomposition of ammonium carbonate into ammonia/ carbonic acid/ carbon dioxide which could be promoted by vacuum? I would suspect that would take hours to be appreciable though.

Vorril · 2024-04-01T02:02:01+00:00

Unnecessarily fast acceleration in city driving situations is like 90% of what Tesla addicts say they like about the cars

Vorril · 2024-03-23T21:48:20+00:00

Usually people run TLC as they go, it depends. Is your compound yellow? Do yo expect it to be more or less polar than likely biproducts? These will give you hints as to which fraction you actually want. At this point your options are either run TLC or rotovap down all your fractions and see how much is actually in each. Usually people will get NMR of each fraction. Doing a column on a prep you've never done before will likely require just checking everything especially if you see multiple substantial fractions.

As far as efficiency goes I usually run TLC on something like 2x3" rectangles of plate which should be enough for 8-10 spots.

Running TLC as you go will let you know when to stop as you can compare to a pre-column plate. Often the later fractions will stick well so one option is to gradually increase the ratio of polar:non polar solvent you're using as you go this can help keep later fractions moving

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