exchemist

Yes, thanks, that's what @joigus told me.

Right. But in gas discharge tubes? I doubt that CuCl2 is used, though if it were I assume it would be to produce a green colour. Krypton glows yellowish-green, I know. (Perhaps that accounts for the rather sickly yellow-green of older French traffic lights.) But, looking this up, I see that many of today's so-called "neon" lighting tubes are in fact fluorescent, relying on a coating on the glass to produce the colour, rather than direct emission from the gas inside. What I am having difficulty tracking down is what fluorescent material is used to produce green. My first guess would be an organic dye. Any idea?

Not quite, it is a proton (and an electron) that you would need to remove from an atom of mercury, in order to convert it to an atom of gold. It is the number of protons in the nucleus (and the corresponding number of electrons to keep it electrically neutral) that determines what element an atom is. But indeed, if you were to remove 2 protons and 2 electrons from a mercury atom, you would have an atom of platinum. N.B. If you were instead to remove neutrons from the nucleus, you would just have a different isotope of the same element as before. It is the electrons that determine the chemical properties that define an element, and the number of electrons goes with the number of protons.

I don't think this is quite right. Magnetism and induction play no part in the operation of a gas discharge tube, so far as I am aware, except to generate the high voltage needed to strike the discharge in the first place. It's simply an electrical discharge that ionises the gas, which then emits light of a characteristic colour as the electrons recombine with the ions. I am also unaware that CuCl2 is used to modify the colour. Can you provide a reference for this? Since the phenomenon is due to atomic emission, I'm not sure that sending a discharge through chemical compounds would do anything other than to excite the emission spectra of the constituent atoms.

Aha. Thanks very much.

I barely remember anything about catenaries, but I thought they were hyperbolic cosine functions, not tangents.

Look it up on the internet. There is no point in anyone here paraphrasing widely available basic science. If you have a more specific issue, by all means come back here and ask about it. If you are not a bot, that is.

I suppose what you are suggesting, in effect, is to develop cyanobacteria with a higher photosynthetic efficiency. From this Wiki article: https://en.wikipedia.org/wiki/Photosynthetic_efficiency there does appear to be scope for that, at least from the thermodynamic point of view. Interestingly, I see from the same article that cyanobacteria, today, are still thought to be responsible for 20-30% of the oxygen generation on the planet, in spite of all plants that now also contribute. So they can make a difference, certainly. I'll let the biologists comment on whether such a thing could be feasible. I imagine one issue would be that we would get a "bloom" of these super-efficient cyanobacteria in the oceans, due to the biomass they would generate from their enhanced photosynthesis. This might - probably would - screw up the ecosystem of the oceans in various unpredictable ways. It feels risky to me.

It is not clear to me what you mean by "slag". How does calling it that add to understanding? Slag is extraneous material, separated from the desired metal in the process of ore smelting, which is a chemical reduction, generally from oxides. So far as I know, it is not thought that a chemical reduction from oxides is how the metallic core of the Earth came to form. The evidence from meteorites seems to me to suggest that iron and nickel exist in space debris already in elemental form.

It's not p² if A and B are not present at the same concentration, which they are not in a buffer solution, for instance. As I say, I suspect the questioner's problem related to something like that. But since they have not been back, we can't know for sure.

Erm the numerator should be the product of the concentrations of the dissociated ions: [ A ]x[ B ]/[AB] = Kd And I think the questioner is asking about the situation in which [A]=/= [ B ] , e.g. an acetic acid/acetate buffer, or something like that. I suppose what the statement in question is driving at is that is if [ B ] << Kd, then the ratio [A]/[AB] will have to be >> Kd, so that when multiplied by [ B ] it gives Kd. But since, for weak acids and bases, K <<1 , it is not necessary for [A] >> [AB] to achieve that. .......I think...... For example, with acetic acid, Kd = 1.8 x 10⁻⁵ = [H+] x [acetate]/[acetic acid]. So if, for the sake of argument, [H+] is also 1.8 x 10⁻⁵, then the [acetate]/acetic acid] ratio would be 1/1. So I too am a bit baffled by the statement our questioner is querying.

Though the findings of that one, non peer reviewed, preprint seem to be contradicted by the link provided in @swansont 's post. As I say, it seems to be a fine balance of very low risks rather than a choice that is obvious. And then the parents might also to consider the increase in risk to themselves from an unvaccinated child bringing the virus home from school.

The decision as to whether or not to vaccinate secondary school age children seems to be quite finely balanced, if one considers only the risk to each individual child. What may tilt the balance in favour of vaccinating them is the reduction it produces in the level of infection circulating in the population as a whole. UK experience is that levels of infection have shot up since the school term started. Throughout this epidemic it has been remarkably hard to get certain segments of US society to recognise that the virus countermeasures are not applied just for the good of the individual, but also for the good of other people who they would otherwise infect. Given that vaccination cannot prevent infection completely, suppressing it by vaccinating this age group as well seems to be a sensible strategy.

From the article it appears the trains have been returned to service, without being repaired first, subject to careful monitoring to see if the cracks develop further, which they have not. So it does not look as if there is judged to be a risk of accidents due to these cracks. (The "yaw dampers" will, I presume, be the dampers that prevent the bogies from hunting at high speed.)

Why can't you do an internet search and contact the numerous companies listed which do this?

As an addendum, when I was on holiday in Tiree last week, staying with a rather back-to-nature niece, she washed some clothes using "soap nuts", a sort of brown nuggets that she put in the machine in a little bag along with the washing. I had never heard of these. It turns out these contain saponin, a triterpene glycoside which, having an oleophilic and a hydrophilic end, is a natural surfactant and has been used for centuries in the Indian subcontinent. Soap nuts come from the soapberry plant, Sapindus. The clothes seemed to be clean and odour-free after washing, though obviously as the soap nuts remained in contact with the clothes until then end, there was not much effective rinsing off of the saponin. (Possibly the lower temperature at the end of the rinse cycle will have reduced the amount leaching from the nuts.) Be that as it may, I have not developed any rashes or skin irritation, so it seems to work fine.

I’d agree that there is entropy in black body radiation, but I’d take some persuading that a solar cell is a heat engine. If it’s not a heat engine then I don’t think Carnot efficiency applies. For instance we don’t apply Carnot efficiency to the electricity production from an electrochemical cell, do we? But you pose an interesting question. I found this about analysing the entropy in solar radiation, which seems to address what you have in mind: https://www.nature.com/articles/s41598-017-01622-6 This does not seem to make any reference to Carnot efficiency, I notice.

Electrons flow in response to a voltage gradient. They do not produce energy when they flow, but transmit it from whatever is responsible for the voltage gradient. So there is no violation of conservation of energy.

I don’t think the issue of *beating* Carnot efficiency arises, because this system is not a heat engine, I.e. it does not rely on converting heat to work. So it isn’t limited by Carnot efficiency any more than, say, a hydroelectric turbine, is it?

There is nothing about nd1 in the paper you linked, so far as I can see, and it has no special meaning that I am aware of. I suspect it has a meaning in the context of the problem you have been asked to solve. I can't comment more without seeing the text of the actual problem you have been given.

Yes, page 21 and 22 describes the standard splitting of the energy levels of d orbitals in an octahedral and in a tetrahedral ligand field, into E and T groups, the tetrahedral case being the opposite way round from the octahedral case. Any text on crystal field theory or ligand field theory will explain how this arises. What's the issue?

I'm sorry but I am not downloading attached files from unknown sources. You will need to post a relevant extract directly in a post. I assume this is something to do with how the energy levels of the d orbitals are split, according to crystal field theory.

ρ = r.(μe²/hbar²4πε₀). So it is r multiplied by a constant, made up of these various physical and mathematical quantities. Yes of course. But none of this is the subject of this thread.

Well no, it is proportional to r, surely? a is a constant, but ρ =r/a, right? By the way, are you in Brazil or Portugal?

Er, I've just confirmed what ρ is.What are you asking? My understanding of the VB model is that you make hybridised atomic orbitals from the atomic orbitals of the free atom and you then attribute bonding to the overlap of these hybridised atomic orbitals with those of neighbouring atoms. This is what your book is saying. Our questioner is engaged in constructing graphs, using some maths software, of these hybridised atomic orbitals, that's all.