# How can metals like magnesium and sodium burn underwater? [closed]

Please answer with as much detail as possible. I can't find the answer anywhere else and I need it for an essay.

Any websites I have found have conflicting answers.

One said that they don't actually burn underwater, rather than separate hydrogen from oxygen and burn at the surface. Another actually said that they do burn underwater because they take the oxygen source from the water. I do not have a specific definition for "burn" (the question itself is my assignment- write an essay answering that question!), so I know about as much as you do concerning the wording of the assignment.

I do know that alkali and alkaline earth metals are generally very reactive with water, and usually result in exothermic reactions.

• Considering that you are an 8th grader, I think you already know all the answer, you are just overdoing it. I am not your teacher, but if you wrote an essay actually pointing out the vagueness of the term "burn", or that are several possible mechanism of oxidation, I would call it a very good job. – Greg Jul 8 '14 at 19:34
• Please stop taking the bait with the "I'm a kid" or "I'm asking for my friend" stuff. This is a homework-type post, and we don't have a policy granting passes to alleged 8th graders. – Todd Minehardt Apr 12 at 16:35

Your last sentence was the key. Metals like sodium and magesium react with water according to the following equations $$\ce{2Na + 2H2O -> 2NaOH +H2 + heat}$$ $$\ce{Mg + 2H2O -> Mg(OH)2 +H2 + heat}$$ Both reactions produce hydrogen gas and a lot of heat. As the hydrogen gas bubbles out of the water it mixes with atmospheric oxygen. The intense heat ignites the hydrogen-oxygen mixture and the mixture continues to burn (possibly explosively depending upon the quantities involved) as long as hydrogen continues to be generated.