Water is composed of oxygen and hydrogen so why can't you set fire to it?

Answer 1

Different ways to consider this ...
If you had hydrogen and oxygen as separate substances, then you could, indeed, burn a mixture of the two. The product of this burning (or combustion) reaction, though, is water, with the two elements (hydrogen and oxygen) now chemically combined.

So by the time you have water, the burning has already been done ... you could almost regard water as being the equivalent of the 'ashes' of burning hydrogen in oxygen ... and fires don't burn their own ashes.

More conventionally we can look at how reactive hydrogen is compared to other compounds, or its affinity to oxygen. Hydrogen exerts too strong a 'hold' on oxygen, once combined in water, for the water to be re-split in a furrther chemical reaction.Under some circumstances we can 'burn water' though - very hot aluminium for example will tear the oxygen from water leaving hydrogen behind - this has caused big problems in the past in naval conflict where water met burning aluminium, releasing free hydrogen which could then caused a secondary explosion.

(By the way not all naturally occuring reactions give out heat energy i.e. they are not all exothermic, JamesL kind of says this in their answer, they are wrong. You need to look at other factors such as Gibbs Free Energy to work out if a reaction is likely to proceed, not simply the enthalpy.

In addition, a better definition of a compound than Ganesh's is 'two or more elements chemically combined (or possibly 'bonded together') many substances which are mixtures are 'two or more components with the very different properties than the constituents ... (consider colloidal substances such as smoke, foams, meringue, cornstarch/water mixtures, and the mixture of vinegar, egg and oil to give mayonnaise ...).

Answer 2

Water is a compound made up of hydrogen and oxygen.

A compound is defined as a substance which is made up of two or more elements (components) which can have properties completely different from the components.

Therefore we cannot set water on fire even hydrogen is combustible and oxygen supports combustion.

You use computer and even don't know this?
You asked this question to get more answers na?

Answer 3

Both Hydrogen and Oxygen are gases whereas Water is a liquid so it is pretty obvious that a fundamental change takes place when the two gases combine to form the liquid just as the ingredients used to bake a cake are completely changed by cooking them together.

Water consists of two atoms of hydrogen and one atom of Oxygen and they are able combine together in such a way that the reactive nature of the two raw materials is suppressed. Not only that but the shape of the molecule they form is such that the molecules are attracted to each other, preventing them from moving apart as gases do and so forming a liquid.

The whole subject is rather complex but if you're interested I'm sure you'll find plenty of information on the net.

Answer 4

Combustion is an oxidization reaction. When Hydrogen burns in the presence of Oxygen water is formed and energy is released. Water is a very stable molecule. Energy must be put into it to separate the Oxygen from the Hydrogen. The process generally used is electrolysis. Water doesn't burn because it is not an exothermic reaction and it is already the stable byproduct of an oxidation reaction.

Answer 5

When something catches fire and burns, it is a chemical reaction. Water consists of hydrogen and oxygen bonded together chemically, so it's chemical properties are different to that of oxygen and hydrogen as elements.

Answer 6

Fire isn't physical. It is energy that results from the reaction called combustion. Someone may note that H2O is a by-product of fire, along with CO2, but fire is not made up of water, per se. Wind is made up of whatever air molecules are moving. Wind is matter (gas) infused with kinetic energy. specifically, wind will probably be 23% oxygen, 70% nitrogen, other gases, ie. the composition of the atmosphere.

Answer 7

Entropy - its why rocks roll downhill.

Hydrogen molecules and oxygen molecules have more chemical energy than water molecules. When hydrogen and oxygen molecules rearrange their bonds to form a water molecule, the energy is released in the form of heat and light. This is called combustion and is possible only because the oxygen and hydrogen were higher in energy than the water. Once the water forms, it has lost the energy which once existed in the hydrogen and oxygen. This is why water does not burn. In other words, rocks do not roll uphill.

Of course, rocks can be pushed back uphill. This means in order to burn water, it has to combine with something higher in energy than both the oxygen and hydrogen which formed it. In other words, the energy lost to create it has to be placed back into it in order to destroy it. Fluorine gas is just such a compound. It reacts explosively with water to form oxygen and hydrogen fluoride. In fact only three gasses support combustion, Oxygen, Fluorine and Chlorine.

//////////// FYI:

Oxygen is actually a toxic, corrosive, poisionous gas, but life on earth has evolved to use its chemical energy. The destructive nature of Oxygen is easily demonstrated by the existance of many bacteria which quickly die if exposed to this gas. Life on earth evolved without oxygen gas, and these bacteria are living the same way the first forms of life did. When plants evolved and filled the atmosphere with oxygen gas, it killed nearly everything on earth which was not a plant. The bacteria which survived were our oxygen breathing ancestors.

Answer 8

because they are chemically combined and have no physical traits of the individual elements. Water is the result of burnt hydrogen with oxygen. You are trying to burn what has already been completely burnt.

Answer 9

It is determined by the fruit or plant associated with a comparison. In the event that you compare a n to a carrot, the carrot is the better of the two nutritional. But since you compare an avocado to the carrot, then an avocado is better. Both equally the apple and avocado, are fruits.

Answer 10

Good old H2O.

Well if you were to pass a current of DC electricity through it you could.

Its to do with the molecular bonds that keep the Hydrogen and Oxygen bonded. Break them and you release them as gas.