Suppose I had 1# of coal and I wanted to burn this coal in a sealed container where nothing could get out. If I were to continue to pump in oxygen as needed even though nothing was let out could I get a complete burn? What might my container look like at the end of the burn. Would it be under pressure even after cooling back down?
Now I take the same container and the same 1# of coal and heat it from the outside not adding any oxygen. Would I still get a complete burn? What would the inside of the container look like when finished?
What’s your container like? I can picture, for instance, an ordinary combustion chamber with a big balloon stretched over the chimney. That seems like it’d fit your criteria, but would be basically the same as one without the balloon.
For the second container, how big is it, and in particular how much oxygen does it already contain? If you don’t have enough oxygen for a complete burn, then you won’t get a complete burn, simple as that. Depending on the amount of oxygen, you’ll either end up with a mixture of carbon dioxide and extra oxygen, just the carbon dioxide, a mixture of carbon dioxide and carbon monoxide, just the carbon monoxide, or a mixture of carbon monoxide and solid carbon (I’m assuming that if you’re heating it enough to autoignite the coal, you’ll also autoignite any soot). There might also be some states where you end up with dioxide, monoxide, and solid carbon; I’m not sure about the equilibrium state here.
That’s exactly what a bomb calorimeter does. It’s a sealed vessel in which a weighed sample is combusted with oxygen to determine the heat value. It’s pressurized with oxygen and ignited by an electrical fuse. The one I’m most familiar with is made by the Parr Instrument Company, but there are others. The ones I’ve worked with use very small sample sizes, around 1 gram of combustible material. To combust one pound of coal you’d need a really large container. I doubt that would be commercially available.
I don’t really have any use for it beyond curiosity as to what would happen. I am curious as to how much weight volume of oxygen would have to be added to burn the 1 gram of coal for instance.
Well, carbon has an atomic mass of 12, and O[sub]2[/sub] is 32, so to completely burn 1 gram of carbon to CO[sub]2[/sub], you’d need 32/12 = 2.6 grams of oxygen. That’d be a few liters, at standard temperature and pressure.
EDIT: Oh, and I’m also approximating coal as pure carbon, in both this post and the previous one. That’s not actually true (it’s a mix of elemental carbon and various high-mass hydrocarbons, plus various impurities), but the real composition varies, and anyway pure carbon isn’t that bad an approximation.
In practice you’d wash down the internals of the bomb and do a titration of the washings to correct for nitric acid formation, precipitate out the sulfur with barium chloride to determine the sulfur content gravimetrically, and correct for the heat supplied by the nichrome fuse wire.
You never want the oxygen to be the limiting factor. The volume of the bomb I used was around 0.35 liters and I would pressurize it to 30 atmospheres with oxygen, so there was never any risk of incomplete combustion with a one gram sample. For samples that were hard to ignite for one reason or another, maybe high moisture or a lot of non-combustible materials I’d use a pellet of benzoic acid with the sample. It was a calorific standard so could easily be subtracted out of the total heat produced.
