exchemist

What if the sky was made of concrete? Forget it. We can't hope to control volcanic eruptions.

Definitely a case of “Don’t try this at home”. Nickel carbonyl is appallingly dangerous to health and carbon monoxide, which you would need, is also pretty lethal.

Show us how you are going about this, first.

What are you talking about?

Per mole of what? If you mean per mole of water, taking water to be the principal component of the human body, then 4.2J raises the temperature of 1g by 1C deg. The MW of water is 18g, so 4.2 x 18 =75.6J raises the temperature of a mole of water by 1C deg. So 63.6kJ would be enough to raise its temperature by 63.6x 10³/75.6 = 841C, if there were no change of phase. I'll leave the rest to you.

Hmm, I see what you mean.

Look up Newton’s shell theorem. That explains why the mass at a radius greater than the location of the red dot has no gravitational effect on it.

Aha, I see. But this is at very high temperatures. In fact, a moment's thought should tell you the reaction won't go at room temperature, because in this system the urea is a supplied as a solution in water. So obviously that is fairly stable. Regarding the kinetics, I imagine you won't need a catalyst if the solution is sprayed into the combustion chamber, or into hot exhaust, at >500C. (Enzyme catalysts would obviously be no use in such a situation anyway.) Also, this is a reaction in which 2 molecules react to generate 3 molecules. The entropy change for such processes tends to be favourable, so the reaction will be thermodynamically more favourable at higher temperatures. (ΔG = ΔH -TΔS)

No, because all the combinations are soluble. Generally you get that type of reaction when one of the possible salts is a lot less soluble than the others, i.e. it has a lattice that is so stable that the ions to prefer to form crystals than stay dissolved. In such a case, that salt will precipitate out, leaving behind the ions it does not need.

Can you link to where in "the wiki" you saw this? All the links I saw say you need an enzyme (urease) to catalyse this decomposition. Here is a procedure for doing that: https://edu.rsc.org/download?ac=12704

All four ions will remain in solution independently. If you evaporate the water, you may get a mixture of NaCl, CaCl2, NaOAc and Ca(OAc)2, since all are stable salts. However, to find out how much of each you get, you would need to determine the free energy of crystallisation (or solution) for them all, as some combinations will produce lower energy states than others, depending on the lattice energy and the entropy change. You may even get mixed salts like CaClOAc, if there is a suitably low energy crystal structure for that combination.

OK I didn't explain this very clearly in my previous post. A shell is a set of orbitals sharing the same principal quantum number, n. All the elements in a given row of the Periodic Table have their outermost electrons in the same shell, i.e. with the same principal quantum number. For example, elements of the second row, starting with Li, have outermost electrons in the n=2 shell. Next there are subshells. A sub-shell is is a set of orbitals having the same principal, n, and azimuthal (or angular momentum) quantum number, l. So in the second row, electrons can go into the 2s or 2p subshells. The s subshells have l=0, p subshells have l=1, d subshells have l=2 and f subshells have l=3. Finally we have orbitals themselves. These are distinguished by the orientation of the angular momentum, which is set by the 3rd quantum number m(l). Each orbital comprises a pair of quantum states which have identical orientation in space, but with opposite spin orientation of the electron. So for example every p subshell has 3 p orbitals, perpendicular to each other, which you can treat as orientated along x, y and z axes. Each one can have 2 electrons in it, one with spin "up" and one with spin "down". In chemistry we tend to treat orbitals as if they are quantum states, each of which can have zero, one or two electrons in it. Strictly speaking they are not, because you need to specify the spin quantum number too in order to define an individual quantum state properly. But since spin orientation can only have 2 values "up" or "down", and since the spatial orientation of the orbital is what is relevant for chemical bonding, it is convenient to think of the orbital as the basic building block of electronic structure in the atom, each of which can accept a pair of electrons.

No, because the question was not adequately specified, as the progress of the subsequent discussion shows.

Sodium bicarbonate is a very weak alkali - a saturated solution of it only has a pH of 8-9 or so. But I imagine some of the dyes may eventually oxidise over time and cease to function, so it may be better to replace it. Universal indicator contains several dyes that change colour at different pH values. There is a Wiki article that is quite helpful:https://en.wikipedia.org/wiki/Universal_indicator

OK, but isn't this the "observer effect", rather than a true demonstration of the HUP?

I suppose you could look at that way. But that's still a bit theoretical, compared to the width of a spectral line. Is there not some classic experiment that shows how increasing precision in position leads to lower precision in momentum (i.e. a broader frequency distribution, or something? How about limitations on focusing a laser beam to a point, or something like that?

Indeed. However the OP seems to be asking for practical examples in which position/momentum uncertainty is experimentally apparent. I can't think of one offhand. Can you? There are classic examples of the related energy/lifetime uncertainty in things such as the width of spectral lines (uncertainty broadening), but position/momentum? Hmm.

Markus, this has taught me several things I did not know. As usual, when you post....😃

There's nothing magic about using 1 molar solution. Sure, 0.5 M would need half the mass in the same volume of solvent. But as far as strength of the acidity goes, if you are using a weak acid the actual acidity of the solution you make, i.e. the concentration of H+, will not be linear with concentration of the acid you add, since dissociation is only partial. It will take place to a greater degree, as a proportion of the acid added, in a more dilute solution, because the equilibrium HA <-> A⁻ + H⁺ will lie further to the right at low concentrations of H⁺ and A⁻ .

You can get inflammation in your larnyx, pharynx etc. with colds, as these viruses make the circuit of one's respiratory mucous membranes, so it could just be that. I have not heard of anything specific to covid of that nature. I expect it will go away. But it's a funny virus so you are wise to stay alert.

Could that be due to a difference in convention?

Yes I mole weighs 192g, so 192g dissolved in 1litre would be a 1 mol solution. So for 250ml you need a quarter of the amount. Not sure where your 1/2 comes in - typo? (250ml is 1/4 of a litre of course, as you correctly imply in your calculation.)

I think you can get drain cleaner which is based on strong acids (some is also based on strong alkali), but I hesitate to suggest you try, as they are fairly nasty if you spill them on you - or anything else. Citric acid has a first pKa of 3.1 whereas acetic acid has a pKa of 4.76, so citric acid is a bit stronger but not much. (For comparison a strong acid such as HCl has a pKa of -6, so in a different ballpark entirely).

I used the term Ac a bit wrongly actually. Ac, strictly denotes the acetyl group, which is CH3CO - so I should have said Mg(OAc)₂. I'm retired and very out of practice, I'm afraid. Probably best to refer to it as Mg (CH3COO)₂ , to avoid getting into a nomenclature minefield. Regarding Zn's apparent low reactivity, acetic acid is a weak acid. At molar concentration (similar to vinegar), only about 0.4% is dissociated into H+ and acetate. If you had a molar strong acid, e.g. HCl, the reaction would be more obvious I think.

Electrons in atoms can be thought of as standing waves corresponding to resonant frequencies, ie. a series of harmonics. In fact the shapes of atomic orbitals are spherical harmonics, akin to the modes of vibration of a rubber ball if you hit it and look at how it vibrates with a strobe light. Each electron occupies a different quantum state. It has to, as electrons are fermions. "Shells" are simply groupings of related, but different states that are possible for an electron to occupy in an atom. Each shell comprises all the states that have the same principal quantum number, n. But n is only one of 4 quantum numbers needed to specify individual possible states. They others are: - l, which denotes the angular momentum and determines which subshell the electron is in (i.e. s, p, d, f etc), - m(l), which determines which member of the sets of s, p,d, f orbitals the electron is in (e.g p(z), d(x²-y²), etc), - and finally m(s) which determines the spin orientation within that orbital. So one can have a maximum of 2 electrons per orbital, one with spin orientation "up" and the other "down". In chemistry, this accounts for the pattern of the Periodic Table of the elements, each row corresponding to the highest occupied principal shell that is occupied, 1st row n=1 2nd row n=2 etc. (cf. Aufbau Principle.)