• Question: if water is mainly hydrogen, then why doesn't it burn?

    Asked by 07gilpinm to Amy, Drew, Julia, Kimberley, Sara on 20 Jun 2011. This question was also asked by hamster.
    • Photo: Sara Imari Walker

      Sara Imari Walker answered on 20 Jun 2011:

      Hello 07gilpinm!! This is really a wonderful question!!

      What we call burning is really what happens when compounds undergo rapid oxidation. For example when gasoline burns, the carbon and hydrogen atoms in the gas rapidly combine with oxygen atoms in the air to form CO2 and H2O. When charcoal or wood burns, it is their carbon atoms combining with oxygen atoms in the air to form CO2. Water is already as oxidized as possible – being two hydrogen atoms bonded to oxygen so it doesn’t burn!

      A related question is why is water good at stopping fires? Well its because it stops to flow of oxygen to the burning material, as such it can’t burn!

      Great question!

      P.S. – Your Einstein pic on your profile is awesome! He is one of my favs!!

    • Photo: Drew Rae

      Drew Rae answered on 20 Jun 2011:

      Hey there. Burning Oxygen and hydrogen to make water is actually a pretty good source of energy for things like rockets. You can think of it as we’ve already got the burning energy from the hydrogen when we combined it with the oxygen to make water. Before it will burn again, we need to separate the two elements again by adding energy, for example by running electricity through it.

    • Photo: Julia Griffen

      Julia Griffen answered on 20 Jun 2011:

      oooohhh I was thinking about this the other day! You can kinda make water burn..

      So water is a product of combustion, Lets simplify things….so if you were to burn something organic, containing carbon hydrogen and oxygen, and burn them (oxidise) completely the products would be carbon dioxide CO2 and water H20.

      So what’s happening when we burn things.. we are breaking bond. We are breaking down the solid fuel source into gases which releases alot of energy.

      Why doesn;t water burn?? well the bonds in water are really strong. Not only do we have the bonds between hydrogen and oxygen in the same molecule. But we also have forces of attraction between two or more molecules. These are called hydrogen bonds… wiki it to find out more… So these strong bonds of water make it very difficult to burn water. Water also has a large heat capacity (which measures how much energy is required to heat it up.) So its very difficult to break the bonds in water so cannot burn it…. traditionally that is…..

      However there are some chemical methods… and dangerous methods… Some chemicals contain negatively charged hydrogen species, we call these hydrides, and these want nothing more than to be neutrally charged and with another hydrogen. They want this so much that they can ‘rip’ a hydrogen from water, breaking the string O-H bond, releasing alot of energy and producing hydrogen gas. We know this is explosive… and well these reactions go with a bang and cause fires, are very dangerous and we avoid them!

      Exciting stuff..

    • Photo: Amy MacQueen

      Amy MacQueen answered on 20 Jun 2011:

      Good question!

      In water hydrogen is bonded to oxygen molecules so doesn’t exist as free hydrogen atoms which are very reactive and therefore burn very easily, often explosively. In water the hydrogen exists in a much more stable form so doesn’t burn.

      Pretty good really since we are mostly water…

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