1. Chemistry

Does anyone know a good message board for chemistry help? (and not simple stuff)

2. you could try sparknotes.com

they have message boards for pretty much everything...chemistry, biology, computer science, math, literature...

3. whats your question, chemistry is my other degree

4. when hydrogen gas is burned in oxygen, how much will the volume change? I can't find this anywhere and I have a ton of chem books

5. pass

6. >when hydrogen gas is burned in oxygen, how much will the volume change?
I could be wrong, but when hydrogen is burned in oxygen doesn't the chemical reaction result in water? If that is the case then the volume change would be equivalent to a gas/water conversion.

-Prelude

7. As water is a liquid, it is denser than gas.
Therefore the volume would decrease by the amount of hydrogen that burn't.
That amount is detirmined by the limiting reactant.

8. >>when hydrogen gas is burned in oxygen, how much will the volume change? I can't find this anywhere and I have a ton of chem books<<

Is the reaction entirely gas phase ie >100C? It's probably best to assume it is; the reaction is exothermic and a fast free-radical one so the product (water vapour) will initially be in the gas phase before it loses energy and condenses as liquid water.

Anyway here's some info that might help out:

2H2+02=2H20

ie 2 moles of hydrogen combine with 1 mole of oxygen to form 2 moles of water. At stp (1 atmosphere (101 000Pa),298K) 1 mole of gas occupies 22.4 dm-3(litres); so if the reaction is gas phase it will be a little over this per mole of water produced - you need to know the mass (or at least the volume,pressure & temp) in order to get a more accurate answer.

Anyway assuming a gas phase reaction 3 moles of reactants ie 4g of Hydrogen + 32g of oxygen combine to form 2 moles of water ie 36g( no surprises there). Or, put another way, roughly 67.2dm-3 of reactants yield 44.8dm-3 of product ie there is a volume decrease.

Liquid water has a density of around 1gcm-3 - so given 2 moles of product ie 36g it should occupy about 36cm-3 in liquid form; so if the reaction occurs above 0C and cools below 100C then 67 litres of hydrogen/oxygen gas mix burns to produce roughly 36cm-3 of liquid water.

You should be able to ratio it out from this discussion when you are confronted with real data that includes weights, volumes and reaction conditions.

Sorry for waffling on - but i'm very very tired and it's been a while since i've done any of this stuff.

9. so the volume does increase? I also knew the reaction, and actually h2 doesn't have to be at that high of a temp because it is a gas at stp, and only a liquid at temperatures close to absolute zero

10. >>so the volume does increase? I also knew the reaction, and actually h2 doesn't have to be at that high of a temp because it is a gas at stp, and only a liquid at temperatures close to absolute zero<<

I sincerely hope that you mistyped 'decrease' when you actually wrote 'increase'. Not one single respondent to this question has even implied an increase in volume.

If you knew the reaction then you should have been able to derive the answer from first principles - as I have done for you, and from memory while half-asleep. I even wrote the result of the reaction that resulted in liquid water in bold text.

WTF are you talking about high temperature? 100C ie degrees celsius(373K) is the boiling point of water: the gas phase reaction I referred to above this temperature is a description where both reactants and products are gases - hence 'gas phase'. And anyway, my discussion of molar volumes implicitly describes gases: the rule ie 1 mole occupies 22.4dm-3 is true only for gases which, of course, you would also 'know' if you had read any of those 'ton of Chem books' you claim to possess.

11. He said that the reaction was occuring at stp. So the gases will only take up 22.41L per mole.
Having just done my half yearly for chemistry I am painfully awear of that differance.

12. >>He said that the reaction was occuring at stp<<

Not originally. He only added that after I offered a complete explanation.

>>Shtarker: So the gases will only take up 22.41L per mole.<<

>>Ken Fitlike: At stp (1 atmosphere (101 000Pa),298K) 1 mole of gas occupies 22.4 dm-3(litres)<<

>>Ken Fitlike: You should be able to ratio it out from this discussion when you are confronted with real data that includes weights, volumes and reaction conditions.<<

No disrespect intended to you, Shtarker, but please re-read the whole thread; you may then have some appreciation for my earlier exasperation.

13. I had meant increase and H2O may be in the gas form. I was just wanting to know if anyone knew any sources that admit that it increases in volume. One of my previous CSE lab partners almost got a degree in Chemistry, before deciding to change majors, and I did once see a book that also said that the volume increased (although I don't remember what it was called). The volume increases due to the type of bonds, since H2 and O2 are linear, and H20 is bent, which is also why ice takes up more space that liquid water. I just want a book that gives me a value that I can cite in a paper, and use when trying to create something using this reaction. I already have a 52nd edition CRC handbook of chemistry and physics, a 12th edition merck index, and a perry's chemical engineer's handbook, but I couldn't find that type of thing in any of them.

14. I had meant increase and H2O may be in the gas form. ... The volume increases due to the type of bonds, since H2 and O2 are linear, and H20 is bent
Look at the reaction: there are fewer moles of product than of reactant. In gas phase, that means a lower volume -- every mole's worth of gas takes up exactly the same volume at the same pressure, regardless of composition and structure.

15. no, it doesn't. that is the stuff you learn in Chem 1 or 2 in college, but it does depend on structure. they just don't want you to have to worry too much about the structure in relation to chemical reactions. Like I said before...I KNOW THE VOLUME INCREASES BECAUSE I HAD ONCE SEEN IT IN A BOOK, BUT I DON"T HAVE THAT BOOK, AND HAVEN"T SEEN IT SINCE.