Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Nivim]

 If something is labeled "volatile" that means it evaporates at relatively low temperatures. So I guess in this case that does refer to the impurities that enter the air, but the image doesn't give you any idea about what it means.

 I am fairly sure you're talking nonesense about the number of reactions; both because of the existence of four-step reactions I learned in introductory chemistry, and because I just did a search for "methane combustion mechanism" (you reminded me of the name, so google, 1st&2nd page, .edu) that came up with 5-11 steps (a sheet for 11 and a paper talking about a 5-9 step simplified reaction). Well, my question is answered. I guess orders do matter when it comes to those reactions; I had this vague idea that there was some other force that made 5-particle collisions probable.

 In your last paragraph it almost sounds as though people wont launch pedantry attacks at you if you don't ask; anyone who reads it who believes they know something about it will respond. Like me.

[Manae]

You can find the full mechanism here. Yes, far simpler systems can be constructed and still be fairly accurate, and that's how most work is going to be done--especially with more complex mechanisms for larger hydrocarbons.

I'm digging deeper into the GRI site, and it looks like they're up to 325 reactions now. Head to here and type "all" in the bottom left box, click the button, and you can have a look at them all.

[Nivim]

 (Links! :] ) Then why did you say it one of the simplest systems?

[Manae]

Well, if you can get a system of [currently] 325 reactions for CH₄, imagine how big it gets with larger hydrocarbons. Each additional atom added to the starting fuel molecule adds dozens upon dozens of possible radical reactions.

[decius]

Also, I can't guarantee this definition, but I believe for matter to be considered plasma it has to be completely stripped of electrons. In essence, it's just a nucleus cloud, and hot due to the energy required to get to that state.

Completely stripped of electrons? Such that N^-6 is an ionized gas, but N^-7 is a plasma? That sounds valid, but how different are N^-6 and N^-7 in terms of physical properties?

And isn't the mechanism of thermoluminescence the same as the mechanism for chemoluminescence, at the atomic level? (electron goes from excited state to less excitied state, gamma emitted with energy equal to that lost by the electron) I thought that the characteristic distribution of blackbody radiation was due to the doppler effect, and the fact that in a large number of hot molecules, many would be moving away from you and many towards. The relative motion of the emitting electron should be added to the energy of the emitted photon.

I seem to recall that there are many examples of low-energy plasmas, which have a color other than red or white. I might be misremembering, or thinking of ionized gases.

[Manae]

I honestly don't know that much about plasmas, so I can't really go deeper into that. I'm not even positive my definition is true, it's just what I've been led to believe. Color-wise, though, I generally think of plasmas as a cyan. (Popping over to wikipedia. the cited definition is "...an electrically neutral medium of positive and negative particles..." There is the claim also that the magnetic field response and high electrical conductivity are the characteristics of a plasma and is the determinate between the gas and plasma phases.)

At the atomic state, yes, the two processes should be the same. The difference is that chemiluminescence results from excitation due to the reaction, while thermo is the release of an excited state trapped in a crystal lattice previously after absorption of high-energy radiation. So, the heat doesn't cause the glow, it just allows it to get out.

[Virex]

Well, if you can get a system of [currently] 325 reactions for CH₄, imagine how big it gets with larger hydrocarbons. Each additional atom added to the starting fuel molecule adds dozens upon dozens of possible radical reactions.

I see some M's in that table, are they for cataclysts? Because that significantly increases the amount of reactions. Also, it's air we're speaking here so you've got a bunch of nitrogen-related and radical forming reactions that only occure at significant levels at such high temperatures.
If you'd look at a reaction occuring at a much lower temperature (say, non-radical catalytic polymerisations or living polymerisations) you'd go down significantly in the amount of reactions that actualy contribute anything.

[decius]

Whoa, don't confuse the primary pathways with the pathways. I'd guess that M refers to a generic metal catalyst, based on very limited knowledge. As far as which ones are most significant... consider each reaction to also be the reverse reaction. CH3 + C2H6 -> C2H5 + CH4 implies that C2H5 + CH4 -> CH3 + C2H6. One of the two will be significant whenever those species are present.

At the atomic state, yes, the two processes should be the same. The difference is that chemiluminescence results from excitation due to the reaction, while thermo is the release of an excited state trapped in a crystal lattice previously after absorption of high-energy radiation. So, the heat doesn't cause the glow, it just allows it to get out.

Wait, I thought heat, at a basic level, WAS the excitation of electrons. I know that the "electron stored in a crystal latice escapes in the presence of heat" happens; thatt is one of the bases of the dosimeters used un nuclear power plants. That light, however, has a distictive profile that is different from that of objects that are simply hot.

[Manae]

M refers to any third body. Literally any molecule could fill in, though the catalyst analogy is proper.

At the most basic level, heat is the transfer of energy between matter; doesn't really have anything to do with electrons. I guess it could cause excitation, but in general would just be an increase in the internal energy of the matter.

[Virex]

At the atomic state, yes, the two processes should be the same. The difference is that chemiluminescence results from excitation due to the reaction, while thermo is the release of an excited state trapped in a crystal lattice previously after absorption of high-energy radiation. So, the heat doesn't cause the glow, it just allows it to get out.

Wait, I thought heat, at a basic level, WAS the excitation of electrons. I know that the "electron stored in a crystal latice escapes in the presence of heat" happens; that is one of the bases of the dosimeters used un nuclear power plants. That light, however, has a distictive profile that is different from that of objects that are simply hot.

Heat is generaly ascociated with collisions between molecules. The energy levels that occur in these collissions are generaly not enough to excite the electrons in a molecule (unless you're talking about blackbody radiation). Most energy, at normal temperatures, is transfered by activating rotational and vibrational modi, or by changing the kinetic energy. It is probably possible to excite electrons via highly excited vibrational modi, so that way some crystals could potentially ionize thermally.

Since electronic energy levels are pretty much exclusive to the near-infrared and higher frequencies, anything that doesn't cause any apreciatble amount of light or UV is probably not an electronic transition, but vibrational or rotational

[decius]

Nitpicking ahoy! (spoilered for off-topicness)

Spoiler (click to show/hide)

A stone golem heated to stone-melting temperatures will have more mass than a stone-cold stone golem. Because energy has mass, and molten rock has more stored energy than just a rock.

I thought you might have been talking about stored or potential energy, but wasn't sure exactly.

Let's assume your stone golem is a sphere of hard granite with a diameter of 10 metres (ridiculously big). That's 524 cubic metres of stone, with a mass of 1220 tons. The energy needed to completely melt those 1220 tons of granite is approximately 3.22e12 joules (3.22 TJ), equivalent to 3.58e-5 g (0.358 µg).

Infinitesimal or not, if it's greater and not equal, it's more mass.

Bullcarp. Can you provide a mass figure for rock golems accurate to fractions of micrograms? Thought not. The above difference means nothing. The difference between individua golems is likely to be orders of magnitude greater.

Further nitpicking.

Spoiler (click to show/hide)

By my research, granite melts (technically it's a mixture, and partially melts, but this is the temperature of granite magmas) at 1533 degrees Kelvin. It has a density of 2.75 grams per cubic centimetre, and a specific heat capacity of 7.90e2 joules per kilogram Kelvin. So a 10 metre diameter golem has the volume you said, of 5.24e8 cubic centimetres and hence a mass of 1.44e6 kilograms. I couldn't find information about the enthalpy of fusion (extra energy required to melt a substance of the right temperature) of granite, so I assumed it was the same as water, 3.34e5 Joules per kilogram (it isn't - water has a ridiculously high enthalpy of fusion because of the hydrogen bonds between molecules, and granite only partially melts). This gives us 1.75e12 Joules for the heating to melting point and an exaggerated 4.81e11 Joules for the melting itself, for a total of 2.22e12 Joules. Mass-energy equivalence still only gives us 2.47e-5 kilograms (kilograms are the SI unit, not grams), or 1.72e-9 percent of the total mass.

Short version: for the temperature of the golem to be at all relevant to mass calculations, you would have to have an extremely precise mass measurement device, far more accurate than anything that will exist in the next few centuries.

And, since heating a substance (generally) causes it to expand, and we know the pressure on the surface of the golem must be normal air pressure, a magma golem will way significantly less than a golem of the same, non-molten stone. Either that or it will be much, much larger.

You didn't do any math to show what fraction of that energy actually becomes mass though. We only get significant contributions to mass in conditions like moving 90% of the speed of light (in which case we're getting mass instead of velocity changes.)

Wait, does temperature itself even ever contribute mass?

Well... no. Heat transfer, acceleration, and phase changes all respect conservation of mass. Only nuclear changes convert mass to/from energy.

As far as the thermal expansion of stone goes, I think stone will expand from 5-15% from room temperature to its melting point. It will weigh slightly less for the same mass, due both to the added displacement of air and to the increased distance to the center of the planet (since it will be taller).

[Sean Mirrsen]

Most of the mass of a molten stone humanoid would likely be concentrated at its legs though,  as flowing stone would be dragged down, so I'd say that last part is negated. Also, it effectively lowers the density of air around it by heating it up (or wait, does it work that way? I think it does, hot air balloons and such).

[EvilTwin]

that would make the golem sink a bit more, which would even be a higher factor than the thermal energy...

thermal energy, btw, is movement of molecules, the hotter, the faster... they are moving in a randomized fashion, the so-called Brownian motion. Since kinetic energy changes the mass (only slighty, i know) of an object, the golem's mass is in fact affected by it.

EDIT: Ok, I'm sorry, wasn't Brownian Motion, but something similar...

[G-Flex]

Most of the mass of a molten stone humanoid would likely be concentrated at its legs though,  as flowing stone would be dragged down

You're assuming the stone would actually flow realistically down, which isn't very valid. After all, we know the creature actually manages to maintain humanoid shape, so how much mass winds up in the legs is fairly arbitrary.

Actually, you'd be able to check in the new raws anyway.

[EvilTwin]

[no offense]

G-Flex, this important stuff! 

No, seriously... I don't really care about the relationship between temperature and weight of a golem, and I don't think the other guys here do. This talk is for having fun, not for being cool. It's still good it has been moved away from the FotF-thread, since that thread shouldn't derail like this or like it did with armor-and-weapon-related stuff the other day, because that one is serious.

So please, don't be a grinch on us. Let us have our fun talking about non-sense and tell yourself that you have grown in mind.