Breaking Up The Water Molecule

Today I watched an episode of Mythbusters concerning pouring water on grease fires. The scenario was a grease fire in a frying pan (8 table spoons of grease) on a gas stove with a mechanical device rigged to drop one table spoon of water onto the burning grease.

Of course, the result was an explosive reaction sending a ball of flame up 10 to 12 feet high and probably 2 to 3 feet wide.

I was surprised at the violent reaction and began to wonder about the possibility that the violent reaction might be actually breaking down the water molecule into hydrogen and oxygen, adding to the fireball potency.

The resulting explosive fire ball just seems way out of proportion to the sum of its parts, being just grease and water.

I do understand the physics of the rapid conversion of water to steam, but this did seem odd to me.

What if this experiment were conducted in a vacuum. There would be no flame in the pan since there would be no oxygen, however, if, when the water dropped into the pan with a resultant flash it would mean that the oxygen and hydrogen were split out of the molecule. What might that mean for hydrogen engines as opposed to hydrogen fuel cells?

A rapid breakdown of the water molecule would be much more practical than the slow electrolysis process used now.

I know, it is probably that I misunderstand what has happened in the experiment, so, someone may be able to explain it to me?

You're misunderstanding the science behind the reaction.

The heated grease is burning because it's being vaporized, this allows the combustion. The small amount of water added is instantly turned to steam that carries with it vaporized grease as it expands hundreds of times it's volume.

There is when you have the flash of fire, but the water molecule is still intact and escapes as a gas. It is not being split into hydrogen and oxygen in any way, it's just acting as a vector to further expand the grease that is already at it's flash point.

reply to post by anxietydisorder


I do understand the reaction of water conversion to steam and the effect it has on the grease as it rises. My question about this is, due to the very small amount of water added, the reaction seems out of proportion.

The tablespoon of water hitting the surface of ignited grease creates a violent and instantaneous conversion of water to steam. But is that all that happens? Could this violent action of the water molecules break them apart? I guess the answer is a simple yes or no (probably "no"). Since the answer is probably "no", is it based on any actual test as opposed to an assumption based on known physics.

Originally posted by Hopup Dave
reply to post by anxietydisorder

 

I do understand the reaction of water conversion to steam and the effect it has on the grease as it rises. My question about this is, due to the very small amount of water added, the reaction seems out of proportion.

Dude, it's called Fuel-Air-Explosive. Nothing new. Read the explanation provided for you.

Breaking up of H2O happens at much higher temperatures and/or in the presence of a catalyst (yes, it's possible).

The bond between the two hydrogen and one oxygen is not broken in this reaction. It simply turns from a liquid to a gas.

I've been out of school for a long time, but if I remember correctly, super heated steam has 1,000 times the volume of liquid water. When I worked on military vessels you always had the greatest respect for steam lines because the pressure and heat could peel the skin off you in an instant if you turned the wrong valve or a line ruptured.

I could tell you some great stories involving steam, but this probably isn't the place or time. Just rest assured that the science is sound, and it's quite likely one of the most tested and understood reactions known to man.

And don't try this at home.
I've had to treat patients with burns and it's painful and ugly for me, and even worse for the patient.:shk: