Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Poisonous and Combustive

  1. Jan 20, 2006 #1
    What makes something poisonous?

    What makes thinks combust "readily" or quickly or slowly?

    How do you know what the reaction will physically look like if you combine two meterials? Like Magnesium + water = a bright fire, etc.
  2. jcsd
  3. Jan 22, 2006 #2
    What we consider poisonous is something that if taken will seriously affect our health and possibly kill us. The chemical, however, is any chemical that is harmful to us. Let's say. we can consider HCl poisinous because it would probably kill us if we decided to drink it.

    For combusting, it is the chemical that actually reacts with the oxygen that determines wether it will burn slowly or fast. For example, water is not a good combustible because the H2O molecule is made of H and O that are so tightly bonded that the hydrogen doesn't want to combust and the oxygen can't combust with itself.

    Hope this helps.

  4. Jan 22, 2006 #3
    Thanks, I understand the combustive part, but I still don't get exactly what makes a substance poisonous? I meant specifically at the molecular level, what is it about the substance's atoms/bonds that makes it poisonous?
  5. Jan 22, 2006 #4
    It's really about what the atoms do or how they bond, but also the specific molecule or atom can be harmful to our health. If you have a harmless molecule, you can transform it into a harmful one by changing the molecular structure. Olive oil, for example, can become carcinegenic if cooked. So you see, there is a little of both, partly the atoms themselves are poisonous, and partly it is the way they bond as a molecule that makes them poisonous. The molecular structure is changed and the substance becomes harmful.
  6. Jan 23, 2006 #5
    How do you know what the reaction will physically look like if you combine two meterials? Like Magnesium + water = a bright fire, etc.

    Study, study, study.......
  7. Jan 23, 2006 #6


    User Avatar
    Science Advisor

    Combustion depends on a lot of things. The main ones I can think of are:
    1) oxidation state
    For example, alkanes burn a lot faster than alcohol. There's probably an exception, but I don't know of any
    2) bond angles
    If the bonds are stressed, the compound is not stable. Something like octanitrocubane is very unstable because the bond angles are forced to be 90 when they should be something like 119.5
    3) multiple bonds
    Things with multiple bonds between carbons burn like crazy. Compare a bottle of propane (blue bottle) to a bottle of propadiene (yellow bottle "mps gas") and you'll see the difference.
    4) volatility
    Ether burns a lot faster than gasoline; volatility is one of those reasons.

    btw, putting magnesium in water does nothing.

    Poisons (and drugs) generally interfere with reactions that should happen in your body. For example, psilocin, the drug/poison in "magic mushrooms", is strikingly similar to serotonin, a neurotransmiter found in your brain. Substitute one for the other and suddenly things don't work too well anymore. It's like putting diesel in a car that uses gasoline.
    Last edited: Jan 23, 2006
  8. Jan 23, 2006 #7
    Substances can be toxic to the human body for many reasons. Nerve gases work by messing with your neurons, causing rapid fire of neurotransmitters across a synapse. This causes muscle convolusions etc. Other reasons for toxicity can simply be because a compound is relatively unreactive in the human body. Benzene is known to cause cancer. Benzene is a pretty inert substance, your body has trouble trying to change it to something it can easily expel. This is also why heavy metals are also very toxic inside the human body. Poisons are bad because they inhibit reactions inside the body. Your best bet is probably to ask this question in biology, or wait for a biochemist, if you want more detail.
  9. Jan 23, 2006 #8


    User Avatar
    Science Advisor
    Homework Helper

    It has to do with the oxygen supply, temperature, and type of fuel. It may be that you're trying to differentiate between a combustion and an explosion here. Have you done any research on explosions and the physical chemistry basis?

    You should refer to the biology forum for the "poisonous query."

    Usually you can analyze the reaction from a rigorous quantum perspective to find all of the details, e.g. the color. Otherwise you can take into account the important physical parameters of the reaction, such as enthalpy, free energy, rate, that every empirical aspect can be explained theoretically.
  10. Jan 23, 2006 #9
    Did my answers help? I'm just trying to be helpful, but I think these guys know a lot more than me.
  11. Jan 24, 2006 #10
    Yes, all the posts helped. Thank you everyone!

    I'll research and read more about it and ask any specific questions I have.

    I was wondering about the combustion thing because, after I saw the Myth Busters episode where they tried to make a rocket with civil war technology, I was inspired and want to make my own.(and obviously, not as big) I'm in the first stage..."the vision" Infact, I'm not that serious about it, its just a vision right now.
  12. Jan 24, 2006 #11


    User Avatar
    Science Advisor

    I saw that episode, but I was puzzled why they didn't use oxygen as the oxidizer. Their excuse was that you can't make liquid oxygen. Be that as it may, you can sure compress the hell out of it. Oxygen tanks have over 2000 psi in them; that's something like 125 atmospheres. It also makes for much better burning than whatever it was they used, I think it was NO2.
  13. Jan 29, 2006 #12
    They used nitrous oxide (N20, laughing gas, NAS!) They're not allowed to tell us how, but Im sure anyone can just google it.

    Man that be so cool to have, feeding it to little kids must be so much fun!
  14. Jan 30, 2006 #13


    User Avatar
    Science Advisor

    You don't need to make it, you just buy it at the store. It comes in cylinders used in cappuccino machines.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook