• Question: If hydrogen is highly flammable, why isn't water?

    Asked by Matthew to Ahmed, Francesca, George, James, Nitheen on 14 Nov 2014.
    • Photo: James Sullivan

      James Sullivan answered on 14 Nov 2014:

      Hi Matthew – great question

      Water is H2O and hydrogen is H (or H2).

      when H2 explodes it reacts with oxygen (O) to form water (H2O).
      That reaction releases loads of energy – hence an explosion.

      H2O on the other hand can’t react in the same way (the H atoms are already bonded to an O atom)

    • Photo: Francesca Paradisi

      Francesca Paradisi answered on 14 Nov 2014:

      In water the two hydrogen atoms are much more stable than in hydrogen gas because they are linked to the oxygen. in hydrogen gas the two atoms are linked to one another and that bond is very unstable. Imagine the hydrogen gas being at the top of a slope and water at the bottom. it takes very little for the gas to tip over and fall down the slide (releases energy, explosion) while the water will not go uphill (needs energy, no explosion).

    • Photo: George Dowson

      George Dowson answered on 14 Nov 2014:

      The shortest answer is that water is hydrogen that has already been burned. It has no further energy to give by combusting,

    • Photo: Ahmed Osman

      Ahmed Osman answered on 16 Nov 2014:

      Dear Matthew
      Again you back with a very interesting question
      The properties of individual atoms change completely when they combine into molecules. I will give a real example life, you know that Every time you salt your food you use NaCl salt, each molecule of salt contains one atom of chlorine (chlorine molecules are a poisonous gas), and one atom of sodium (sodium atom itself explodes on contact with water!) but when you combine chlorine and sodium it give you a compound with totally different properties with safe like salt and you can add it in your food.
      For water the process of burning in this case is the oxidation of hydrogen or combination of the hydrogen and oxygen molecules. The result of the oxidation of hydrogen, its combustion product, is simply H2O or water. The reason that water (in any state) is not flammable is that it is already the product of combustion.

      The chemical equation for this reaction is: 2H2 + O2 -> 2H2O.
      Hopefully this answer is clear