exchemist

OK, why do you think precession means additional kinetic energy, rather than just partitioning the existing kinetic energy between motion about two axes? What work is done? Take me through the logic.

That, frankly, is a stupid reply, given everything you have been told.

Ah but what "kinetic energy of precession" is this? On reflection I don't think there is any. I think the phenomenon of precession merely re-allocates the existing angular momentum into motion about 2 axes, doesn't it? The energy change results from the change in potential, due to the alignment/anti-alignment of the magnetic moment to the field.

"Magic happens" is not in any textbook I have ever seen. I stress the idea of precession is a semi-classical analogue for what happens quantum-mechanically. As I say, my understanding is that some of the atoms gain energy from the applied field and some lose it to the field, depending on which M state they are in. This is reflected in the idea of kinetic energy of precession but, as that is a semiclassical analogue, you can't take too far. The analogy works intuitively for those states that are raised to higher energy by the field, but doesn't work so well for those that are lowered in energy. If you take a single atom, the field changes the potential experienced by the electrons in the atom. They no longer just experience a spherically symmetrical electric potential from the nucleus, but also a linearly polarising magnetic potential as well. They either gain potential energy from the field or give up potential energy to the field, depending on orientation. This is presumably what is responsible for the force and consequent deflection they experience as they pass through the field. I don't think there is any need to presume they have to radiate.

You have asked this type of question several times now and the answer has been the same in all cases: consider the solubility of the possible combinations of ions. There is an article in Wiki on this: https://en.wikipedia.org/wiki/Salt_metathesis_reaction Note especially the section on counterion exchange, which is what your questions have been about. There is also a link in the article to a quite useful solubility chart, which is helpful if one does not know whether a given ionic compound is appreciably water-soluble or not: https://en.wikipedia.org/wiki/Solubility_chart

This is yet another commercial plug from SCIRP, a Chinese publisher pretending to be located in California that is suspected of predatory practices: https://en.wikipedia.org/wiki/Scientific_Research_Publishing

The mechanism in the Stern Gerlach experiment is as written up in the textbooks on QM, surely? My understanding of this, admittedly from my 1st year as an undergraduate, 50 years ago, is that the atom precesses at the appropriate Larmor frequency for the M state it occupies, and carries on doing so indefinitely, unless it encounters radiation of the right (i.e. Larmor) frequency to stimulate a transition to a different M state. Regarding energy conservation, what I think happens is that those states with an antiparallel component (of magnetic moment: due to the -ve charge on electrons the magnetic moment points in the opposite direction to the angular momentum itself) - acquire energy from the field, while those with a parallel component give energy to the field, the net effect being zero, in line with conservation of energy. However, once the states are split, statistical thermodynamics enters the picture, causing the ones in the higher states to tend to lose energy and drop down to lower states. As I say above, I think this relaxation process will be primarily non-radiative, because of the improbability of spontaneous emission at such low frequencies. Non-radiative relaxation will manifest itself as heat in the material. So no, I do not think there is significant radiation emitted in the Stern-Gerlach experiment. But I'll be interested to see if anyone else has a different view. P.S. Be aware, too, that the notion of precession is a semi-classical one. In QM, only the compment of the magnetic moment or angular momentum along the field z-direction is defined. The orientation of the component in the x,y plane , i.e. the component that "rotates" in the precession model, is undefined. This is a consequence of the uncertainty principle (non-commuting operators)

When a compass needle aligns with the Earth's magnetic field, are you telling me it emits radiation?

Nope, you emphatically do not get classical EM radiation. This is a quantised system. Please read my 2 previous posts. We can get onto spin-echo EPR later, once we have agreed on the basics.

Yes, that's why the angular momentum quantum number is called J rather than S. The values of J can be any integer between L+S and I L-S I. The total angular momentum of the atom is √(J(J+1)).h/2π. But you need to be careful with applying classical radiation concepts in QM systems. Recall that the Bohr model of the atom failed because classically an electron in orbit around the nucleus, being an accelerating electric charge, should radiate, lose energy and fall into the nucleus. Which it doesn't. Hence the move to Schrödinger's quantised model of orbitals, in which the electron can only radiate by making transitions between a small number of discrete, allowed energy levels, determined by solutions to his equation. Exactly the same is true in the case of the space quantisation we are discussing here. The atom can only move between discrete allowed energy levels, denoted by different values of M, the quantum number for the allowed projections of the angular momentum along the field direction.

According to my (admittedly rusty) understanding, the only way an atom can radiate in this situation would be by transitioning between the different allowed space-quantised energy levels, i.e. for an atom with angular momentum J, between the 2J+1 values of M, the quantum number of the projection of the angular momentum vector along the field direction. Absorption of energy to bump up electrons from lower energy to higher levels is the basis of EPR (known as ESR in my day). The splitting of the energy levels is modest and therefore these energy transitions absorb (and emit) photons in the microwave region of the spectrum. I'm not sure I follow what you mean by spin alignment being the result of radiation. The alignment simply occurs as an external field is applied. But, to pursue your line of thought, in the absence of a field there will be equal numbers of atoms in each of the M states, because they are degenerate. When the field is applied, this is no longer so and the atoms will adopt a Maxwell-Boltzmann distribution among the energy levels of M, with more in the lower (more aligned) energy levels and fewer in the upper (more anti-aligned) ones. This, I suppose, must involve either emission of microwave radiation or non-radiative relaxation processes. I have never seen this described and don't know which is dominant. However as the Einstein transition probability for spontaneous emission goes up with the cube of frequency, it may be that spontaneous emission processes in the microwave region are so infrequent as to be negligible. But maybe someone else here, ideally with experience of EPR, will know. According to my old Herzberg, the energy, W, of the states in an applied magnetic field is W(0) + hoM, where W(0) is the energy in the field-free case and o is the Larmor precession frequency. That implies that for transitions between adjacent energy states, (i.e. for which ΔM=1,), ΔW = ho = hν, i.e. the microwave frequency of the emitted or absorbed photon is the Larmor precession frequency. I'm not sure if this deals with your query, but maybe it's a start.

Yes, Coyne is on a bit of rant in his response. I sympathise with him to some extent, but there may be a bit more behind the article than he gives credit for, in the context of past educational practice in the Southern USA.

I'm not sure I'm following all this. But the study of chemistry at university level - and the subsequent professional practice of it, academically or in industry etc., which is what the article seems to be about, is a discipline of science distinct from pharmacy, which is about the medical application of drugs (and obviously a fortiori of medicine). Also the article is specific to the USA - and possibly to the states south of the Mason-Dixon line, as it emanates from East Carolina University, which is in North Carolina. So I don't think the racial or sexual makeup of UK medical courses, or of London retail pharmacy staff, has a great deal to do with it. Nor is Margaret Thatcher's choice of degree subject evidence of much. There was a handful of Somerville chemists in my year and some more from St Hilda's, but as there were only 5 women's colleges, we were over 80% male - much to my chagrin, though I did eventually acquire a physicist girlfriend from St Anne's. The colleges went co-ed one by one, from the end of the 70s, I think. (In fact, that is evidence of how, until recently, women were so poorly provided for at the ancient universities, probably because of the hangover of their original monastic foundation.)

It's an English figure of speech. If I had known English was not your first language, I would not have used it.

I can't follow your logic, I'm afraid.

.......thus enabling junaid.alemdar to hand in his or her homework two years late. 😁

I'm afraid this is incomprehensible. And yes, using the laws of thermodynamics is what we all do in science and they have never failed yet. So if your idea relies on breaking those laws, we can state with confidence it won't work. But if you are able to explain your design clearly, with diagrams, we may be able to identify where your error lies.

In London most of the pharmacists seem to be of south Asian descent. But they are not chemists, not having studied chemistry, contrary to popular British English vernacular.

OK, I can easily understand arguments that the composition of the practitioners of a science may be racially skewed, but that is hardly "white supremacy". But I can see where some confusion can arise. I had read it as claiming that the science itself has a racial bias, i.e. there is something about the theories of chemistry that is racist. That really would be bonkers. But maybe, indeed, all they mean is that white men are disproportionately represented among chemists in the US. That would not be a surprise. I expect the same is true of lawyers and linguists.

I quote below the abstract of a recent paper from E.Carolina University, published last November in the Journal of Chemical Education, which has attracted the scorn of Jerry Coyne. This article presents an argument on the importance of teaching science with a feminist framework and defines it by acknowledging that all knowledge is historically situated and is influenced by social power and politics. This article presents a pedagogical model for implementing a special topic class on science and feminism for chemistry students at East Carolina University, a rural serving university in North Carolina. We provide the context of developing this class, a curricular model that is presently used (including reading lists, assignments, and student learning outcomes), and qualitative data analysis from online student surveys. The student survey data analysis shows curiosity about the applicability of feminism in science and the development of critical race and gender consciousness and their interaction with science. We present this work as an example of a transformative pedagogical model to dismantle White supremacy in Chemistry. While I've no doubt that some of the chemists of the past may have had racist views, or benefitted somehow from slavery, or committed the sin of being men, or whatever, I really struggle to think of anything in the subject itself, or how it is taught, that could have racial connotations. Does anyone understand what they can be thinking of? Or is this just as bonkers as it appears?

TESCO is hardly upmarket. I shop there quite a bit - but then I don't think I have an inferiority complex. 😁

No, an endothermic reaction absorbs heat. The rest of your post doesn't seem to make sense

OK all sorted out now.

By "unique perspective" you mean "barking mad", I presume? 😁

Forgive the question, but why do you want to do it this way rather than using a pH meter?