exchemist

No. Read the post by @TheVat. The difference is that a 40kg rock is not aligned with the skeleton to load it in the same way as body weight would. Furthermore it is dead weight, unlike body weight, which is a mass of bone, fat and muscle that moves dynamically in response to the action of walking. Both things make a huge difference to how the knees and other joints are loaded, during the action of walking or other movements. (It is noteworthy that people used to carrying heavy loads in many parts of the world choose to place them on their heads. This will be because having the extra load taken by the spine is the best way to avoid off-centre loading of the joints.)

I think he has been asked to graph them, to see how the shapes arise from the linear combinations, or something.

Yes it would need to be either green hydrogen, by electrolysis, or blue hydrogen (from methane but with CCS). Some are sceptical that blue hydrogen actually achieves the goal, by the time losses of methane (a powerful greenhouse gas) etc., are taken into account. But it seems to me one can't be too choosy at the start: the main thing is to get something at commercial scale in place and see where imaginative people can take it. Home heating is a hell of an issue and nobody is tackling it at the moment. Where is the Elon Musk of central heating, eh? I've looked at heat pumps, but since the cost/kWh of electricity is 4 x that of gas in the UK, it's tough to make that stand up economically, even in terms of running costs only. When you factor in the higher capital cost and the possible need to change radiators in the house due to the lower heating water temperature, or else the need for a conventional booster heater to get it up to the temperature for the existing radiator system, it makes no sense. Regarding hydrogen embrittlement, I don't know about that, but I am old enough to remember that we used to run "town gas" (basically synthesis gas: CO + H2) through all the gas mains in Britain before "North Sea gas" (methane) came along in the 60s. It seemed to work. When N Sea gas came in, a guy from the gas board came round to change over the burners on our gas cooker - and that was it.

My understanding is that hydrogen may have a place for heavy goods vehicles, for which battery weight could be prohibitive. Hydrogen is also being talked about - and piloted - as a full or partial replacement for gas in home heating. Keele university has a pilot in which hydrogen is blended with natural gas and burns successfully without the need for changing burners: https://www.keele.ac.uk/discover/news/2020/june/hydeploy-update/pilot-positive-results.php This currently only blends it in at 20%, but that still saves a lot of carbon emission and equally importantly provides a pathway, using existing infrastructure, for the commercial production of hydrogen to get started. We will need a low-barrier way to break into hydrogen production or everyone will just wait for everyone else. No one will build trucks until hydrogen supply exists, no one will put in refuelling points until trucks are built, etc., etc.

Yes you have a point there. But the young family stage is quite brief. I'm in a quandary myself about a new car. I really only use it for visiting my aged father in his nursing home once a week, which I could do by bike and train if I had to, and for our annual trips to Brittany. I have no actual need to keep stuff permanently in the car. So maybe I'll go electric in a couple of years, or maybe I won't get one at all and just use Zipcar when I need to take stuff to the rubbish dump etc, as my friend does. The peak demand issue I don't see as invalidating the approach. Given that I am talking about cities, there is little need for commuting by car. Furthermore, catering for demand peaks via a collective pool of vehicles obviously requires far fewer than one per household. I'm not sure I understand the safety issue you raise. You seem to be base this on reducing vehicle weight by cutting back on the safety of the construction. I don't think anyone in this thread has suggested such a thing, and certainly not me.

This is intellectual masturbation.

If you really need the full solutions, then these will involve the product of the Laguerre functions (expressing the radial wave function) and the spherical harmonics that express the angular dependence. You should be able to find these on the internet for 2s, 2p, 3d etc. but I confess I don't know where. Here is an explanation of how they are used: https://demonstrations.wolfram.com/HydrogenAtomRadialFunctions/ As you can see, it is not simple. I did an entire quantum chemistry supplementary subject at university without being required to master exact solutions. The reason is that exact solutions are only possible for the hydrogen atom. For multi-electron atoms and molecules one has to resort to approximate solutions anyway, so it is far better to focus on symmetry properties etc., rather than getting enmeshed in the algebra of analytical solutions. So I'm still a bit sceptical that anyone expects you to get into all this. Like @studiotI too think it would be a good idea if can post the text of the task you have been assigned (if it is in English - or maybe I could decipher it in French).

I'm not suggesting anyone will police anything. There is no need to go off the deep end like some Republican anti-masker (only kidding😄). I'm suggesting that in cities - I did say cities- I can easily see driverless cars, that you summon like a taxi, could replace private car ownership for a lot of people, if it is done well. As my previous posts have pointed out, the elements are already there: services such as Uber and Zipcar are already popular. (Zipcar and Uber have systems to clean cars, obviously. It works already today. So this objection is not real.) As @CharonYpoints out a few posts up, Singapore and New York already show the trends I have in mind. Once it works well in the cities, it can expand from there. Don't forget also that the next generation of potential car owners - people like my 18yr old son- are questioning very seriously whether they should have a car at all, due to environmental impact. I think we could underestimate the extent to which the new generation is willing - eager, even - to do things differently from their fuddy-duddy, climate-destroying parents.

Not a good analogy, I think. Zipcar already offers a service whereby you hire a car by the hour when you want one. I have a friend who does this in preference to the cost and bother of owning her own car. If you live in a flat, in a row of terraced houses, which is true of much of Victorian London for example, car ownership is distinctly a mixed blessing. Parking is already a problem. Having to charge an electric car in the street will be even worse. If you add to that the convenience of not having to drive the bloody thing, you can go to a party and have a few drinks, or watch a film or something while you are in transit. Sort of like Uber, but without the risk of getting raped, or catching Covid from the driver. I would agree this makes most sense in towns and cities, but I can see it coming quite fast, with electric vehicles. Sure. At the level of the individual vehicle, the first thing must be to get away from heat engines, limited as they are by Carnot cycle efficiency constraints. While a lot of electricity is still generated by fossil-fuelled heat engines today, they are a lot more efficient than a car engine. Renewable generation sources, which are growing, avoid the problem. A hydrogen vehicle could be powered by a heat engine, which won't be any more efficient than today's vehicles, or by a fuel cell system, which should be better. But currently, hydrogen generation is itself inefficient, so I understand, unfortunately.

Haha. Actually I do have time for philosophy, in principle. For instance, one needs at least a bit about the philosophy of science to explain its key features to those that don't know. But the argument in this thread does strike me as something of an exercise in staring up one's own arse, I must admit.😀

Any argument that concludes no=yes is self-evidently wrong, so the only value in it [yawn] is trying to spot the error. Apart from anything else, if you argue no=yes, you will have the Me Too movement down on you like a tonload of bricks, and quite rightly.

By not requiring everyone to own one, for a start. It's grossly inefficient use of resources, when you think about it. I think that driverless cars, that you summon when you need one, would be a far more efficient system.

Aha. Good to see you run up the Jolly Roger at last: now we know what we are dealing with. Quantum Mechanics is a "construct" in the same sense as Newton's Laws. All theories are constructs, in that they extrapolate from observations to make general inferences - which are then tested against further observation. It is not "blind faith", because these theories are based on observation and tested against observation. So we know they work. That is the polar opposite of "blind faith". You appear to be attacking something here, without first taking the trouble to try to understand it. Is this wise? And, if you think such "constructs" can't tell us anything, I'll be intrigued to see you put forward a theory that is not a "construct" in this sense.

Are you trying to provide evidence for the proposition that philosophy is a waste of time? 😁

Oh really? I think it is because he is scared.

There is also some bleaching effect from sunlight, which can help remove stains that the detergent does not quite deal with 100%. I've observed this with white table napkins, for example. So there could be a bit of an old wive's tale about this, due to the superficial appearance of cleanliness due to UV bleaching.

© Rex Tillerson 2017 😃

Yes, there are well understood reasons for why these energy states are what they are. This is what Quantum Mechanics tells us. QM also tells us how it is that electrons moving between states, or molecules moving between vibration or rotation states, or whatever it may be, can emit (and absorb) EM radiation. This was all sorted out in the 1920s and 1930s, actually, when QM was being originally developed. So it has been widely known for about a century and is taught to all physics and chemistry undergraduates - and even in simplified form in schools, in the 6th form. You really need to read a bit about this before coming forward with ideas of your own. Otherwise you risk trying to reinvent the wheel, from a position of ignorance, which is obviously going to be asking for trouble.

I'm not entirely sure what you are really asking. It's probably a language issue. I doubt that you are being asked for the full algebraic expression for these wavefunctions. It seems more likely that you are being asked to show how linear combinations of appropriately chosen atomic orbitals generate the hybridised ones. This link shows you how 4 sp3 hybrid orbitals can be constructed from s and 3 p orbitals: https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Map%3A_Inorganic_Chemistry_(Housecroft)/05%3A_Bonding_in_polyatomic_molecules/5.2%3A_Valence_Bond_Theory_-_Hybridization_of_Atomic_Orbitals/5.2D%3A_sp3_Hybridization You can do something analogous for the others. By all means come back if I have misunderstood.

The thing you need to keep in mind is that light is always emitted by a source. The wavelength (frequency) is determined by the source that emits it. For example the famous sodium D lines, which make street lamps yellow, are due to sodium atoms emitting a pair of frequencies in the yellow region of the spectrum because the emission is due to electrons in sodium atoms dropping from a pair of levels in the atom to the ground state. But if you look at the tungsten filament in a lightbulb, that emits a continuous spectrum, because this is due to radiation due to thermal motion, rather than transitions between specific energy levels in the atom. Alternatively a radio antenna emits radiation of far longer wavelength (lower frequency), corresponding to the frequency of the oscillation of electrons in the antenna. So it's all to do with the source of the light.

I assume that would be the value FOB. On a CIF basis the value would be considerably less. I wonder if it would even have any +ve value after shipment cost is factored in.

No, this would be a waste of money, for the reasons others have given. For towels in particular, so long as they are hung up where they can dry after use, they will generally last for a week before they need a wash, if only used by one person. After all, people dry themselves with them when they are already clean, right? So they don't pick up contamination very quickly. But if they are allowed to stay damp they will start to smell after just a day or two. Modern hotels do not change towels every day any more, because of the waste and environmental impact. They nearly all ask the guest to put the towel in the bath if really they need a fresh one, and otherwise ask you to keep using the same one. As others have pointed out, there is no need to sterilise clothes or towels. Your body is designed to cope with ordinary domestic micro-organisms without trouble.

Washing soda will have some ability to saponify fats, whereas soap simply emulsifies them. Strong alkalis are often useful in the kitchen at cleaning fats that have degraded and become sticky and resistant to detergents. Oven cleaners are a good example. I'm not sure of the chemistry of these degraded fats (maybe someone else here will know), but it seems that alkalis can still saponify them. Washing soda is not as strong as caustic soda for that (and by the same token is considerably safer to use), but probably quite a bit better than bicarbonate, I would think.

If you heat NaHCO3 to 200C you will indeed decompose it to Na2CO3: 2 NaHCO3 -> Na2CO3 + H2O + CO2. You have effectively been making ordinary washing soda by a rather wasteful and expensive route. Since washing soda will do a better job than baking soda (sodium bicarbonate), why not just buy that instead?

I'm a little confused by this discussion. I always thought that washing soda was Na2CO3, sodium carbonate, rather than NaHCO3, sodium bicarbonate. That would be a stronger alkali than bicarbonate and presumably more effective at reacting with fatty acids or even saponifying fatty material.