water liquidity , why at room temp. ?

Discussion in 'Chemistry' started by river, Aug 29, 2011.

  1. river Valued Senior Member

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    why is the molecule of hydrogen and oxygen liquid at room temp.

    when both can only be liquid at extreme low temps. below -256 C for oxygen and -236 C for hydrogen

    what is chemical explaination ?
     
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  3. wellwisher Banned Banned

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    Once the water molecules forms; H2O, the H2O molecules will interact further with each other via what is called hydogen bonding. Hydrogen bonds are not only electrostatic between opposite charges but will also have partial covalent bonding characteristics. This causes neighboring water molecules to bind together like a very weak covalent bond. The result is the liquid state at much higher temperatures than expected by a molecule so light.

    The reason ice expands when it freezes is also connected to the hydrogen bonds. The partial covalent bonding nature of hydrogen bonds requires that the orbitals for the hydrogen bonding have a sweet distance for interaction. This cause the molecules to push apart so the partial covalent bond can become optimized. If we add pressure to ice, we can turn it back into liquid. This occurs because we will compress the water molecules smaller than their optimized covalent sweet spot distance. The result is more of the weaker polar interactions; no longer solid.
     
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  5. river Valued Senior Member

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    but before the H2O molecule forms and /or is forming what is the mechanisum that allows this molecule to form

    as we know neither the hydrogen or the oxygen atom becomes a liquid at room temps.
     
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  7. origin Trump is the best argument against a democracy. Valued Senior Member

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    The formation of water from hydrogen and oxygen has nothing to do with the temperature at which the these three substances form liquids.

    Fill a room with 2 parts hydrogen and 1 part oxygen the gases will not react. Walk into the room and try to light a cigar. The gases will almost instantly convert to water. They will most likely locate your remains quite a distance from the point of original ignition. That is because there is a certain amount of energy that is needed to break the bonds of Hydogen and oxygen and allow them to recombine to water. The formation of water is extremely exothermic so the heat released from the each subsequent water molecule formation will allow more hydrogen and oxygen to form water in a sort of cascade affect.

    But like I said this mechanism has nothing to do with the condensation temperature of any of the three materials.
     
  8. Trippy ALEA IACTA EST Staff Member

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    The precise mechanism of the combustion reaction between hydrogen and oxygen takes place by a series of pathways involving radicals.

    As has been pointed out before, this comes down to the nature of the bond between hydrogen and oxygen, within a water molecule, once it is formed.

    The bonds between two hydrogen atoms are neutral because the electrons spend most of their time between the two atoms, or in other words, spend eual amounts of time around each atom.

    The electrons in the O-H bond 'like' spending more time around the oxygen than they do the hyrdrogen, the oxygen, is, in essence, greedy, it keeps the electrons around it more than the hydrogen does. Because the electrons spend more time around the oxygen than the hydrogen, we see the Oxygen as having 'more' electron density then it should, and the hydrogen as having 'less' electron density then it should, which in turn means that we see the hydrogen as having a slight positive charge, and the oxygen as having a slight negative charge.

    Because this imbalance exists in where the electrons spend their time, the Hydrogen in one water molecule finds itself attracted to the lone pairs of electrons on the oxygen atoms of neighbouring molecules. It wants to form a bond, like a normal covalent bond with them, but it can't manage it, because although the hydrogen has a slight positive charge, it doesn't have enough of a charge to form a full bond, although sometimes the hydrogen can 'jump ship' and move from one water molecule to another, which is why water has a neutral pH - it has equal amounts of H[sub]3[/sub]O[sup]+[/sup] and HO[sup]-[/sup].

    This, in turn, is one of the factors that determines waters boiling point, and freezing point. Water is light, so we expect it to have a low freezing point, and boiling point, indeed, Ammonia, Hydrogen Fluoride, and Hydrogen Sulfide are all gasses at room temperature, however, because water can form these strong bonds between water molecules, which makes it harder to seperate the water molecules. and the harder it is to seperate the water molecules, the higher the boiling points and melting points.

    Does that help?
     
  9. arauca Banned Banned

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    I have the impression at certain ratio of the two gases they will react without a spark
     
  10. origin Trump is the best argument against a democracy. Valued Senior Member

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    That would be news to me.
     
  11. arauca Banned Banned

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    http://i1200.photobucket.com/albums/bb337/Wylos/DSCF7799.jpg[/IMG][/QUOTE]


    Explosion Characteristics of Hydrogen-Air and
    http://conference.ing.unipi.it/ichs2005/Papers/120001.pdf

    An ignition wire was used

    Samuel Glasstone P.Chemistry second rdition page 626 shows changes in pressure if the gasses initiate combustion or explosion
     
  12. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    Which means there was a spark.

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  13. origin Trump is the best argument against a democracy. Valued Senior Member

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    Right, when you said without a spark I assumed you meant without a heat source. I also assumed you meant STP. If you rapidly increased the pressure you could also get a mixture of hydrogen and oxygen to ignite; ala dieseling.

    The bottom line is that you need an energy source at STP to initiate a mixture of hydrogen and oxygen reaction.

    edited to add: In my job we use hydrogen as a carrier gas in a >1000F reaction chamber. If the chamber overpressurizes (not anymore we fixed it) the gas would vent out of the chamber. 1000+ degree pure hydrogen hitting the atmosphere will wake you up in a hurry. It sounds like a 12 ga shotgun going off by your head! No spark needed just the heat of the gas was suffincient to initiate the reaction.
     
    Last edited: Aug 31, 2011
  14. arauca Banned Banned

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    Thank you no ill intent of my part
     
  15. origin Trump is the best argument against a democracy. Valued Senior Member

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    No problem, I did not take it that way at all! I thought this was a good discussion.

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  16. river Valued Senior Member

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    hmmm...

    please explain what your saying

    explain these pathways involving radicals
     
  17. wellwisher Banned Banned

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    The H2 and O2 flame is extremely hot. The result is before H2O can form, Hot and reactive fragments will form called radicals. These are very reactive and will attack more O2 and H2. As everything moves down an energy hill, in terms of potential energy, we finally get H2O which is at the bottom of the energy well.

    The reason this reaction is so energetic is oxygen will try to complete its octet of electrons. To do so, it needs two more electrons. Although oxygen will have more negative charge than positive charge and have electrostatic repulsion, the magnetic addition is more powerful. It can get these electrons from hydrogen, but only in terms of sharing them via covalent bonds. This sharing makes the hydrogen slightly positive and the oxygen slightly negative. This results in secondary attractions between water molecules which give it it's unique physicsl properties fr such a small molecule.
     
  18. Nasor Valued Senior Member

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    It always makes me cringe when people explain chemical reactions by saying that the atoms "want" things or "try" to do things. It usually doesn't really explain anything, because obvious the atoms don't actually "want" or "try" anything. But, whatever...
    It is electrostatic attraction that causes the negative electrons to stick to the positive nucleus until the octet is full. The electrostatic repulsion is between the electrons, but the overall electrostatic potential energy of the electrons+nucleus system is still lower when the electrons are stuck to the nucleus (until the octet is filled, at which point adding more electrons causes the electrostatic potential energy to go up). Magnetic interactions don't really have anything to do with it; the energy involved in the magnetic interactions is trivial compared to the energy involved in the electrostatic interactions. Magnetic interactions don't really become significant until you get to the d and f orbitals, and even then, it's usually a pretty subtle influence.
     
    Last edited: Oct 28, 2011
  19. wellwisher Banned Banned

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    The reason orbitals have opposite spin electrons is this allows magnetic addition. Same spin electrons will repel. Both have the same electrostatic repulsion, but magnetic addition will be the deciding factor whether the electrons can share the orbital.

    If we you take two wires with current, the movement of charge will set up a magnetic field. If the two wires have current moving on opposite directions the wire will attract due to magnetic field attraction. This is a basic physics experiment.

    Getting back to oxygen, when oxygen gets two extra electrons to complete its octet, all the P electrons are moving in opposite directions in each P-orbital and each orbital is orientated in 3-D to the others (x,y,z). This gives extensive magnetic addition among all the electron currents. This stability is created even before we add the attraction to the protons.

    Maybe your misunderstanding of orbital magnetisim is connected to you thinking in terms of magnetism being only something we see in iron, and not in terms of any moving negative charge creating a magnetic field. That is why we call it the electromagnetic force; electrons are always in motion.
     
  20. Walter L. Wagner Cosmic Truth Seeker Valued Senior Member

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    Yeah, and my plants 'like' to be watered, and 'dislike' being over-fertilized, etc.

    We tend to try to explain things by putting our emotions into the object of explanation.
     
  21. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    Highly unlikely.
     
  22. Nasor Valued Senior Member

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    No, an orbital has electrons with opposite spins because of the exclusion principle. It has nothing to do with magnetism.
    No, it is energetically favorable for electrons in a given subshell to be around other electrons with the same spin, due to exchange interactions. This is why, for example, all the electrons in a half-full subshell will tend to have the same spin.
    This just isn't ccorrect
    I don't know what you mean by "moving in opposite directions."
    You appear to be attempting to describe exchange interactions, but you're getting it wrong. Exchange stabilization happens between elections in the same subshell with the SAME spin, not opposite spin. See Hund's rule. And as was already explained, these interactions are pretty trivial compared to the electrostatic energies involved.
    No, I can assure you that the I don't imagine electromagnets when I'm thinking about electron interactions around a nucleus...I think about my p-chem textbook.
     
  23. wellwisher Banned Banned

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    In terms of energetics explain why oxygen can form oxide or O-2 while say potassium can not. What is the force that allows more negative charge to exist near a nucleus that there is positive charge, but not for every atom? I knew the empirical rules, I am asking for the logc of the mechanism.

    It can not be electrostatic or all atoms could form -2 and be stable. There has to be more. The EM force is the unification of electrostatic and magnetic with these two forces, interchangeable, since the sum is a single force called the EM force. I will let you answer.
     

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