exchemist

But you can't explain the nature of science without philosophy. I am constantly having to refer to philosophical ideas when trying to explain to creationists what science is and - just as important in such discussions - what is not science.

Do you have a source for the latter statement? I can’t recall coming across such a comforting assessment of the effect of climate change.

There are lots, for instance as shown here:https://www.sigmaaldrich.com/GB/en/products/analytical-chemistry/photometry-and-rapid-chemical-testing/test-strips-papers-and-readers I don’t know of one for discriminating between alcohols, but there is one for glucose, which uses a meter to detect the amount of gluconic acid generated by reaction with blood glucose.

Didn’t you start a thread on all this back in 2008? What’s different now?

Then you are poorly informed. Any sports trainer who is any good will be careful about red-lining it. Most training regimes are largely aerobic and do not proceed to exhaustion. I have rowed most of my life and even rowing training is a controlled mix of exercise that is mainly aerobic. We were also told never to train if we were not feeling well. It has been known for decades that training when you have flu can give you irreparable heart damage for example.

Not heat capacity but Latent Heat of Vaporisation of water, i.e. the heat absorbed in turning liquid water into vapour. This is very high for water, due mainly to the need to break hydrogen bonding between water molecules as they break away from the liquid.

Just leave it. Someone else may came along and add something. They don’t normally get closed unless a moderator considers the discussion has become pointless or objectionable.

Well, there are fuels that makes use of the bond energy of nitrogen, which seems to be the idea you are pursuing. Hydrazine for instance (H2N-NH2) has an enthalpy of combustion of 620kJ/mol, i.e. about 2/3 that of the N-N triple bond, and that is partly because it forms N2 as well as water when it burns, converting an N-N single bond into the triple bond. Hydrazine is also used as a rocket fuel without combustion, being decomposed by a catalyst into N2, NH3 and hydrogen. Again the formation of N2 is responsible for a large part of the heat output. But you can't separate nitrogen into atoms and store it in that form for fuel. That can't be done. By the way, I see you are still at school. I thought you might be. The reason I went into the thermodynamic equations was just in case you were starting to work with them in school - and because I thought it might be fun to apply them to this problem of yours. It is the kind of thing you will learn about if you study chemistry in the 6th form, at about the age of 16-17. If you have not got to that stage, don't worry.

It's not that simple, because it's to do with the statistical distribution of kinetic energy among the atoms and molecules and how that alters with temperature. But certainly there would be a lot more atomic N, if nothing else were going on at such enormously high temperatures (see later in the post). There are two formulae in chemical thermodynamics which enable us to work it out. The first I've already mentioned: ΔG = ΔH - TΔS. We now have the values for this reaction, so we can say ΔG = 945 x 1000 - (16400 +273)x115, which gives a value of ΔG = - 9.75 x 10⁵ . (I add 273 to the temperature as it needs to be absolute, i.e in K rather than deg C.) The second formula is ΔG = -RTlnK, where K is the equilibrium constant, in this case (p(2n))²/p(n2), p(2n) being the partial pressure of atomic N and p(n2) being that of molecular nitrogen. So lnK = - ΔG/RT = 9,75 x10⁵/(8.32 x (16400 +273)) ~ 7. So that makes K ~ 1000. So there will be approx √1000 times, i.e. about 30 x, as much atomic N as molecular N2 at that temperature........ ...or would be, if there were no other processes set in train by such an astronomically high temperature. However, at such a temperature you would no longer have entirely nitrogen atoms! The 1st ionisation energy of N is 1400kJ/mol. You would have a lot of N+ ions and free electrons, i.e. a plasma. This temperature is about 3 times that of the surface of the sun ( refer @chenbeier 's earlier post ). So there you have it. The bonding in nitrogen is so strong that to break it you need to start breaking up the atoms themselves and have to resort to stellar temperatures. Best to look elsewhere for a practical way to store energy.

There is no magic temperature at which the bonds suddenly break. At any given temperature, molecules have a statistical range of velocities. When you dissociate a substance by heating, what happens is some of the molecules get enough thermal kinetic energy for the bond holding the atoms together to break. If a dissociated atom later on encounters another dissociated atom then, unless the atoms have between them more energy than the bond energy, they will recombine. So what you have is a dynamic process, in which some molecules are splitting into their constituent atoms, and some atoms are recombining into molecules. This is a chemical equilibrium: N₂ <-> 2N. Whether most of the substance is in the form on the left hand side or the form on the right hand side depends on the bond energy, the entropy of the two states and the conditions (temperature and pressure). As you raise the temperature, the average velocity of the molecules increases. That means that the fraction of them with an energy greater than the bond energy increases. This results in a greater fraction of them being in the dissociated state at any given moment. A strong bond energy favours the left hand side, while a significant entropy of dissociation favours the right hand side, more so at higher temperatures. What I am pointing out is that - because the bond energy in this case is so high - it is not until you reach about 9000C that you will have equal amounts of molecular and atomic nitrogen. In fact, I've now got a more accurate value for the entropy of dissociation, 115J/K-mol, which leads to temperature of more like 8200C for a 50:50 mixture of atomic and molecular nitrogen. (This is in good agreement with @studiot's earlier post in this thread, in which he quoted a textbook saying that at 8000C, there would be 40% dissociation.) By the way, catalysts are irrelevant to this. A catalyst does not change the thermodynamics of a reaction, which is what determines the equilibrium state. It just accelerates the rate at which it gets to equilibrium from an initial set of reactants. In the Haber process, the catalyst accelerates the reaction by avoiding having to dissociate the nitrogen molecule into atoms before reacting with hydrogen. It does this by forming new bonds between nitrogen and the metal surface. The energy of the bound molecules and atoms stays lower, throughout the process, than if they had to be free atoms. As a result, a greater fraction of the molecules have enough energy to react - so it goes faster.

Well, let's first of all see if our poster is now satisfied with the answers we have given, or if he or she wants to go somewhere else with the topic. It is, after all, a chance to discuss some chemistry.

Quite right, so you did. I've just filled in a few more details for our poster, to help him or her understand why it is not what he or she thinks. 🙂

Not really. The way you describe it misrepresents the mechanism of this reaction. This is the Haber process. The N2 molecule is adsorbed on the surface of the catalyst, where it forms a kind of nitride with it, first end-on and then sideways-on, which then reacts, still on the surface, with adsorbed H to form an adsorbed NH, NH2 and finally NH3, before desorption of ammonia occurs. At no stage are free N atoms produced. This is not a route to formation of atomic nitrogen.

Where do you get 500C from, though? If we look at the equilibrium N2(g) <-> 2N(g), this will be in balance, with similar amounts of N and N2, when ΔG = 0. Since ΔG=ΔH-TΔS, that will happen when TΔS= ΔH, which will be at the temperature at which where T= ΔH/ΔS. ΔH =945kJ/mol, but according to what I have been able to dig up, ΔS seems to be around~100J/K-mol. That would imply an absolute temperature of 945 x 1000/100, 9450K, which is over 9,000C, well above the boiling point, repeat boiling point, of iron!

I think this will be condensation, from periods at which the temperature of the table and cover goes below the dew point of the ambient air. An uncovered table would also develop moisture, but the presence of the cover will hinder its re-evaporation when it warms up and/or the relative humidity drops. Typically, objects will get somewhat colder than the ambient air at night, as they radiate in the IR. This is especially pronounced when there is no cloud cover, so that there is no balancing IR radiation coming back down from the clouds. This explains for example why you can get a ground frost on clear winter nights, even though the air temperature can be 3-4C above freezing. So if the relative humidity is close to 100%, a table or other exposed surface may, for a while during the night, have a temperature below the dew point.

My understanding is that a router emits a stronger RF signal than a cellphone. Whether RF radiation at such levels can really pose a health hazard seems to be a matter of debate. Traditionally it was thought it had no effect on biological tissue, but I think there have been a few studies that challenge that assumption. Maybe someone else here knows more.

In what context?

There's a converter here that tells you how to get from a pressure to the corresponding altitude: https://www.mide.com/air-pressure-at-altitude-calculator

What evidence is there for these sound particles?

That's what I mean: fuel storage is energy storage. Fuel is a just source of chemical energy, after all.

You could, but using a highly compressed gas at over 500C might not be the most convenient or efficient form of energy storage.

I would think with DNA certainly cosmic rays will be one source of mutation, so they will have a role in evolution. With neurons I would think not. Neuronal processes do not seem to rely on individual molecules, in the way that genetic coding does. So damage to one molecule won’t affect their operation, I would have thought. The energy cosmic rays impart to organisms as a whole is tiny. But for an individual atom in an individual molecule, it is enough to break its bonds, tear off electrons, knock it out of position etc. Of all biological structures it seems to be only genetic material that relies on a single (very large) molecule. That’s why cosmic rays can make a difference there.

OK, I've looked this up and to be honest it is a bit confusing, between the collision rate for an individual molecule, total collisions for a given absolute number of molecules and a total collisions per unit volume. Also, a lot of the formulae are for reactions between 2 different species, so they are for molecules of type A colliding with molecules of type B, etc. But as far as I can see, and simplifying the formula as far as possible, it looks to me as if, for a gas consisting of a single type of molecule, the total number of collisions expected in unit time per unit volume is: Z = 2N²d²√(πkT/m), where: Z is the no. of collisions per unit volume per unit time N is the no of molecules per unit volume (i.e. number density) d is the effective diameter of the atom or molecule for interacting in a collision (atoms and molecules are not hard spheres of course) k is Boltzmann's constant m is the mass of the atom or molecule T is absolute temperature (The derivation of this formula is extremely hairy, by the way, as it has to allow for the fact that all the atoms of molecules are moving in random directions.) You can use 2 x atomic radius for d, which will be good enough for an approximate answer (order of magnitude). You can see the number of collisions goes up with the square of the number density, and with the square of the atomic or molecular diameter, and with the square root of temperature. Number density is fairly easily obtained from the ideal gas equation PV=nRT. I mole of any (ideal) gas occupies 22.4l at STP, viz. 273.15K (0C) and 1bar pressure. But I don't know what you are going to do with this information. You won't stop N atoms recombining at any practical temperature or pressure. In fact, if your idea is to use separated nitrogen atoms as an energy store, that can release energy when N2 is re-formed, I think you are better off to segregate the N atoms in molecules that when suitably brought together generate N2. For instance, ammonia is now talked about as a future fuel for ships. More about ammonia combustion here: https://www.sciencedirect.com/science/article/pii/S1540748918306345

Catalysts reduce activation energy, not increase it. Collision rate - that’s a kinetic theory question. You would also need to know the effective diameter of the atoms, but I’m sure that’s available. I’d need to think how to do that when I get out of bed and have moment later in the day. Someone else may offer an answer in the meantime.

Absolute zero and less than 1 mTorr.😁 Seriously,, forget it. There is almost no activation energy for this recombination. So you can only slow it down by lowering the rate of interatomic collisions.