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    A mixture of hydrogen and Oxygen doesnt react until it is ignited with a spark then it explodes. The energy of a spark is tiny yet enough to ignite any quantity of Hydrogen/Oxygen mixture suggest an explination for this.

    Is it becuase its very energetically unstable so a little flame is enoug to give it the activation energy required?
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    (Original post by hazbaz)
    A mixture of hydrogen and Oxygen doesnt react until it is ignited with a spark then it explodes. The energy of a spark is tiny yet enough to ignite any quantity of Hydrogen/Oxygen mixture suggest an explination for this.

    Is it becuase its very energetically unstable so a little flame is enoug to give it the activation energy required?
    Basically yes.

    Oxygen and Hydrogen together do not have enough energy on their own to overcome to activation enthalpy so need a "boost", which n this case is a flame.
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    (Original post by hazbaz)
    A mixture of hydrogen and Oxygen doesnt react until it is ignited with a spark then it explodes. The energy of a spark is tiny yet enough to ignite any quantity of Hydrogen/Oxygen mixture suggest an explination for this.

    Is it becuase its very energetically unstable so a little flame is enoug to give it the activation energy required?
    ... and following on from above... once one molecule ignites, it produces enough energy to overcome the activation energy of the neighbouring molecule and more, and the process repeats exponentially; a chain reaction, until all of the energy is lost as heat in the atmosphere.
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    A nice demonstration is putting some platinum wool in a glass jar of hydrogen. The catalyst lowers the activation energy and allows the reaction to occur with the energy provided at room temperature.

    It's a chain reaction. The spark provides sufficient energy to cause some of the molecules to react, the exothermic reaction of these molecules provides energy to the nearby ones and enables these to react, and so on! The process is so fast that it appears that the whole thing is igniting at the same time.
 
 
 
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