Domain: chemguide.co.uk
Stories and comments across the archive that link to chemguide.co.uk.
Comments · 7
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Re:IANA Physicist, So...
Seriously, look at the reaction process for what you're talking about
... you'll notice there is no reaction without adding oxygen ... in the form of water.Did you even bother to read the article you linked to? LOL. It clearly states that it oxidizes several metals. It then goes on to describe the reaction that you're trying to claim is the only oxidation case. In fact, the article you linked lists at least four chemical oxidations above and beyond those involving metals.
You seem to only capable of reading about the ones that have to do with water. Rather selective of you.
But hey, don't let basic chemistry stand in your way of looking silly.
Don't let basic reading skills stand in your way of looking silly [sic].
YOU CAN NOT OXIDIZE WITHOUT OXYGEN.
Yes, you can. The article you linked points this out to you as well.
LOOK AT THE DEFINITION OF OXIDIZE.
You appear to be obsessed with the colloquial definition of 'oxidize.' You should check out the formal definition; especially the part that relates it entirely to electron transfer.
See the stupid people who agree with me:
http://www.chemguide.co.uk/ino...
Don't just read the first part (the beginners' definition), read down to the "most important use of the terms oxidation" part...
Maybe I should have typed that in all caps so you could read it...
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Re:Just Basic Organic Chemistry...Catalysts lower the activation energy for a reaction...
That's not "exactly" true. The catalyst provides an alternative route for the reaction with a lower activation energy.
Here's an analogy from chemguide to drive home the distinction:Suppose you have a mountain between two valleys so that the only way for people to get from one valley to the other is over the mountain. Only the most active people will manage to get from one valley to the other.
Now suppose a tunnel is cut through the mountain. Many more people will now manage to get from one valley to the other by this easier route. You could say that the tunnel route has a lower activation energy than going over the mountain.
But you haven't lowered the mountain! The tunnel has provided an alternative route but hasn't lowered the original one. The original mountain is still there, and some people will still choose to climb it.
In the chemistry case, if particles collide with enough energy they can still react in exactly the same way as if the catalyst wasn't there. It is simply that the majority of particles will react via the easier catalysed route. -
salt - water heat exchanger: tricky
Here is a shorter, and in my opinion, more informative summary. They're heating up sodium chloride salt, then using that to produce steam from water, which drives turbines. That's nice, because molten salt is fairly nasty stuff to work with.
Anything has its chemical activity rise exponentially with temperature (the Arrhenius equation) so as things get hotter, they get more chemically aggressive. Molten glass will dissolve bricks and mortar. Molten sodium and chlorine ions are even nastier -- a sodium ion is a very small object, only a little larger than hydrogen -- and can diffuse into metals, weakening them and creating leaks. -
Re:Byproducts
If you heat things up enough, you'll break down even dioxin. All you need to do is dump in enough energy to start breaking the (fairly stable) molecular bonds. This is what dioxin looks like. A chemist can tell you why it's so stable: lots and lots of alternating single/double bonds. quick chem lesson: lines drawn between atoms, in this case the angles on the outside of the structure, representing a carbon atom at each angle, are single bonds, drawn C-C-C (or in this case
/\) while double bonds are drawn as two lines: C-C=C. Something with alternating bonds, C-C=C-C=C, acts as if it has about 1.5 bonds between each, which is tremendously stabilizing. Benzene is a ring of six carbons, with six single and three double bonds: alternating single/double bonds, so it's drawn as a hexagon with a circle in the center, to symbolize its electron structure. This has two benzenes, with oxygens connecting them. Because the oxygens have electron pairs that are unused in bonding, but are in the right place, they can act as, essentially, parts of double bonds, meaning the center section is also alternating single/double bonds -- or, more correctly, the whole works has evenly distributed electron density. Whew. here is some more stuff about aromatics and the stability of benzene.
The bond energy of carbon-carbon bonds in benzene is about 200 kJ/mol (as I recall: I may be wrong); dioxin is (I think) going to take more energy to break. But at any given bond energy, a given temperature with large excess of oxygen, over a given time, will break a certain percentage of the dioxins down into smaller (and quickly oxidized) byproducts, so all you have to do is establish what's a reasonable level of dioxin to release into the atmosphere (which a person could justifiably argue is "zero, dammit!") and make sure your flame temperature is high enough that you transfer more energy than that threshhold to the exhaust stream. The temperature of flames is really spectacularly high -- the free air temp of burning oxygen and hydrogen is something like 5500 degrees F -- but you have to guarantee that the mass of the exhaust actually gets that hot, so you have to care about heat transfer, not just temperature. In any case: this is well-known chemistry. It is possible to burn dioxins and destroy 99% (or 99.9% or whatever you've decided is 'enough') of them.
The sulfur would become sulfur dioxide, which would be captured in scrubbers, the way they do in steel plants and coal-fired power plants. They use the captured material to make sulfuric acid, and sell it at a major profit, even considering the initial cost of installing the scrubbers.
That's probably WAY more than you ever wanted to know, but I like chemistry. -
Re:Short synopsis for the lazy
people can't google for VDW if they don't know what it means
Actually, they can. He said held together weakly by vdw...bonds. I googled "vdw", and the 7th result was intermolecular bonding - van der Waals forces, anybody with half a brain (and slashdotters generally aren't too dull) could easily figure out that that is what they want. You don't even have to scroll the page to see it. -
Re:Interesting name.. haven't heard it before...There's a good article on van der Waal forces here.
Unless, of course, you're just being sarcastic, in which case disregard this comment.
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explanation is right
Basically the fluctuation causes a temporary dipole, which induces a complementary dipole in the neighboring atom, which causes the usual dipole-dipole attraction (but on a much weaker scale than when there are actual permanent dipoles, like with water).
Some additional explanation with some diagrams is available here.