Subject:
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Re: Quick physics question
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Newsgroups:
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lugnet.off-topic.geek
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Date:
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Sun, 16 May 1999 08:42:08 GMT
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Viewed:
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143 times
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> If you take a sealed container with nothing but pure water, and you heated it
> enough -- assuming the container withstands the heat and pressure with no ill
> effect -- will the oxygen and hydrogen eventually separate? At some point,
> will the container hold just free hydrogen and oxygen molecules (H2 and O2)?
Eventually you will get a plasma, composed of neucleii and some electrons. At
that point it's not really relevant to talk about compounds, what you have
is basically soup. From memory you can't dissociate most simple molecules
before they become plasma, and water would have to be one of the worst - it's
so far down the energy pit/so stable.
Note that I know very little about plasma physics, just a sort of "New
Scientist" level idea. The details of the transitions and energies involved
are a bit beyond me.
> Would you have molecules or atoms?
> Would the fact that you have twice as many hydrogen atoms than oxygen atoms be
> significant?
Yes, in that it's very, very hard to contain hydrogen atoms. You would not
be able to use a physical container for the heating-to-plasma step above, it's
either magnetic or inertial confinement (like the fusion things - wee glass
spheres full of whatever, hit them with lots of laser beams. They heat up
so fast that the atoms don't have time to escape before the temperature
reaches fusion levels. (Or at least that's the idea)
> Would you be able to form ozone (O3)?
In the question of what compound you get, plasmas don't really form compounds
in the sense that normal matter does. It's sort of like asking what the
interior of a black hole is made of, or perhaps what the pH of the core of
the sun is. Think of it maybe as mixing balls covered with with hook velcro
and balls covered with loop velcro. Start with a few balls of loop velcro,
then add a pile of smaller balls of hook velcro. If there are very few of
them in the box they will form lumps of regular sizes (a loop ball covered
in hook balls being the most common one). If you shake it up a bit you'll
get lots of those things, plus probably a few loose hook balls that don't
have any big loop balls to join on to.
Now, if you keep jamming balls into the box and shaking it eventually
the whole lot is going to agglomerate into one big lump.
Now, imagine the loop balls are oxygen. A gas has very few balls in the box,
so mostly you have the stable ball configuration - each oxygen is covered
with hydrogen, and there are no big messy lumps (peroxide, ozone etc).
As you keep shoving more balls in (increased pressure) and shaking the
box (temperature), you''l get more of the lump compounds and eventually
just one big lump. That's plasma. At least in this analogy.
> Then, if the container were cooled down to a temperature where steam can exist
> again, would the hydrogen and oxygen then ignite (back to H2O)? Would this
> combustion increase or decrease the pressure inside the container?
Almost certainly, but it depends on how you do the cooling/condensation
process. If you just turned off the magnetic confinement then you'd likely
get hurt, I mean, end up with a cloud of steam.
Now, if you cool the plasma slowly and carefully eventually it will click
over to a hot, pressurised gas, and probably that gas will be mostly water.
Simply because that's the most stable of the available compounds. Stable
here meaning "not explosive". Hydrogen, oxygen, peroxide and ozone are
all nasty reactive gasses, which means they react easily with "stuff" to
form more stable compounds.
For gasses, PV = nRT - Pressure x Volume = nR x Temperature (where n =
quantity of gas(es)), so you could work it out by assuming two steady states,
one with the hydrogen/oxygen mix, the other after the explosion. The problem
is that you have several things happening to create the condensing plasma,
one of which is cooling (you're changing the "T" term above). So that
equation doesn't really apply, except to tell us that cooling the plasma
will tend to drop the pressure or volume of the gases. So yes, burning
the H/O mixture will make it hotter, but cooling it will offset that.
I guess it does tell you that your cooling will need to remove more energy
than just the thermal energy of the plasma plus the state change energy,
it will need to remove chemical energy of the burning too.
HTH
Moz
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Message has 1 Reply:
 | | Re: Quick physics question
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| (...) Well PV = nRT only applies to an ideal gas - it just doesn't happen in real life - there is another equation for a real gas which escapes me right now. R = 8.31 the gas constant. (...) Dunno about that. (25 years ago, 17-May-99, to lugnet.off-topic.geek)
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Message is in Reply To:
| | Quick physics question
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| Hey all, Just a quick question, or series of questions, but it'll keep me up all night if I don't find the answer. :-, If you take a sealed container with nothing but pure water, and you heated it enough -- assuming the container withstands the heat (...) (25 years ago, 15-May-99, to lugnet.off-topic.geek)
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