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Name: Brandon
Status: student
Age: 12
Location: N/A
Country: N/A
Date: Around 1999


Question:
Dear Sir or Madame,

Right now I am doing a science project on why water doesn't burn. The reason I ask this is because if water is made up of the two extremely flammable elements hydrogen and oxegyn why won't it burn? I have made the prediction that the reason it doesn't burn is beacause it is a liquid and liquids don't actually burn but the fumes do. I have searched my local library and I can not find anything.Thank you for your time.


Replies:
When something burns it combines with oxygen. Water is the result to hydrogen "burning"... it already combined with oxygen. You really could say that it already burnt and therefore will not burn again. A simple answer.

Larry Krengel


You have asked an interesting question. You are clearly thinking. I can tell you exactly what the answer is, but that would ruin your science project. Because your science project isn't about finding out the answer to a specific question. After all, your teacher could probably do that right away for all the kids in the class and save a lot of time. No, the reason you have the science project is to practise finding out answers by yourself, so that later on you don't need a science teacher. So, instead, I'm going to talk about how you could answer your question yourself.

What you have now is a ``hypothesis.'' You have imagined a possible reason for water not burning. What you must do now is test the answer. That means you must try your best to prove your hypothesis wrong. If you succeed (your guess is wrong), then you make a new guess and try again. If you fail, no matter how hard you try, then you might have the right answer.

Does that sound like a lot of work? It is! But, unfortunately, that is the only way we know to get right answers that we are SURE are right. It is so easy for people to talk themselves into believing things, even crazy things, that if we just decided answers that SOUNDED right probably WERE right, we'd make terrible mistakes all the time. Many things that seemed reasonable have turned out to be wrong, and many things that seemed absurb turned out to be Gospel truth. It's a sad situation.

How can you prove your hypothesis wrong? Any way that works is OK with science. The only important rule is that your way has to be reproducible. That is, someone else must be able to do exactly what you did and get the same result. That's so we know you didn't get your results by accident.

Here are some standard methods:

(1) Show the hypothesis is illogical. Your hypothesis is logical: ``(1) Wet things don't burn. (2) Water is wet. (3) Therefore, water doesn't burn.'' But sometimes people come up with illogical hypotheses, which we can disprove right away, such as: ``(1) Water is blue. (2) Sapphires are blue. (3) Therefore, water is made of sapphires.'' We don't need to know anything about water or sapphires to know that this hypothesis is illogical, and the conclusion is wrong, or, if right, right only by accident.

(2) Show that the premises of your hypothesis contradict observed fact. The ``premises'' are the things you assumed to be true in the beginning of making your argument. What did you assume was true at the beginning? Well, you assumed that no liquids burn. Can you find a counter-example, an example of a liquid that burns? I'm guessing you can (gasoline, alcohol, lamp oil, lighter fluid), because you made the extra statement that fumes (near) a liquid do burn. That is, you say it isn't the lighter fluid that burns on the charcoal, but the fumes near it. So your argument must be refined, like so: ``(1) Liquids do not burn, but fumes near them do. (2) Water is a liquid but has no fumes nearby. (3) Therefore, water does not burn.''

Can you now think of a fact that contradicts (1)? That is, a liquid with no fumes nearby, that burns? Or, can you think of a fact that contradicts (2), that water is a liquid with no fumes nearby? What would water fumes be like? How could you find out if any were near some liquid water? Can you use the same method you would use to find out there are fumes near liquid lamp oil?

(3) Show that at least one of the predictions of your hypothesis contradicts observed fact. In this case, you have concluded that water does not burn because it is a liquid with no fumes nearby, and these do not burn. Let's try to figure out some other predictions of your hypothesis. How about: if you could water fumes, they would burn. Can you get some water fumes and check?

Grayce


Brandon,

One thing to consider in your investigation is how water could be formed in a chemical reaction.

If you burn hydrogen (H2) in the presence of oxygen (O2), the reaction would follow:
   2H2  + O2  -->  2H2O

This reaction releases a substantial amount of energy. If you have ever seen old video of the explosion of the Hindenburg (a "blimp") you can imagine the energy released as the water is formed.

Consider now trying to "burn" water...that is, trying to break it down in the presence of oxygen to some other materials. You can see that since a lot of energy is released in its formation, a lot of energy would have to be provided to drive the reaction in the other direction.

This is only a clue, not a direct answer to your question. Note that as water is formed a lot of energy is released. It is therefore a very stable material. Thoroughly heating it, while supplying energy, does nothing but produce steam of the water (water vapor) and does not break the substance down. Try investigating the strength of the bonds present in the water molecule, and for some other interesting investigating, look up the topic 'electrolysis' in which water can be broken down back into hydrogen and oxygen by providing energy in the form of leads from positive and negative battery terminals. Naturally, don't do any kind of investigation at home without first discussing this with your teacher; you run the risk of shock when working with a battery around water and should not do this without your teacher's assistance. NEVER work with an electric wire around water; this can be deadly.

Thanks for using NEWTON!

Richard R. Rupnik
Internal Quality Auditor
Lucent Technologies


Water doesn't burn because it's already an ash. You are correct that water is made of oxygen and hydrogen, and you are also correct that hydrogen is flammable. However, oxygen is not flammable. Oxygen is an oxidizer, that is, it supports combustion. A jet of oxygen will NOT burn in air! When oxygen and hydrogen are mixed, they can chemically combine, generating lots of heat energy. When this reaction is complete, the product is water. So, water is what is created when hydrogen burns.

Richard Barrans Jr., Ph.D.
Chemical Separations Group
Chemistry Division CHM/200
Argonne National Laboratory


Dear Brandon,

The fumes of water are called steam. Does steam burn?

What does it mean for something to burn? Chemically, it means that a chemical reaction occurs between a fuel and an oxidizer to form a new chemical. The chemical reactivity of the product is very different from the starting chemicals. In this case, the starting chemicals are hydrogen gas (H{2}) and oxygen gas (O{2}) [the curly brackets indicate that the numbers should be printed as subscripts]. The product is water, H{2}O.

This can be written as:
             H  + O   -> H O
              2    2      2  < ---These are supposed to be
subscripts and indicate the number of atoms of each element.

When no subscript is given it is assumed to be a 1. Since water is the PRODUCT of burning hydrogen it cann't be made to burn further

Greg Bradburn



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