Molten salt + water = boom

[RainDreamer]

So why did the water suddenly go boom in such a short time? I know the expansion of superheated steam would cause some minor explosion, but this is just massive boom in such a short time frame.

[Findthepin1]

Does it work in space?

[Tex_NL]

13 minutes ago, RainDreamer said:

[Snip]

So why did the water suddenly go boom in such a short time? I know the expansion of superheated steam would cause some minor explosion, but this is just massive boom in such a short time frame.

I am actually quite underwhelmed. I expected a much bigger explosion.
But you have already answered your own question. The extreme heat of the molten salt flash-boils some of the water. And since water is incompressible the energy is passed directly to the glass.
If you want a BIG boom you throw a cup of water in a pot of boiling oil over an open flame.

[Hannu2]

Steam explosions work in space but energy of such explosions are low compared to typical rocket propellants. If he had combined for example few deciliters of hydrazine and N2O4 there would not have been anything left of camera and poor guy.

[StrandedonEarth]

Molten salt is basically dissociated  chlorine and sodium.  Sodium loves to strip the oxygen out of water molecules, leaving behind heat and hydrogen in the process. Kaboom!

 

i remember a science teacher throwing chunks of sodium or potassium (separate experiments; normally stored in oil) into a metal wastebasket full of water then covering it with a piece of plywood, which would then get blasted 15 feet into the air. 

[mikegarrison]

As mentioned above, the key is that water is incompressible.

[AngelLestat]

I guess the answer more close to the true is from StrandedonEarth.
The heat does not have much to do, more than just provide the energy needed for the chemical reaction.

In case the heat is the only effect you will saw the Leidenfrost effect, which prevents the fast heat transfer, you can see objects drop in water that are much more hot (2500c) and nothing happen.

Edited March 9, 2016 by AngelLestat

[Vim Razz]

1 hour ago, StrandedonEarth said:

Molten salt is basically dissociated  chlorine and sodium.

"Dissociated" is a pretty strong term in this case, but the jist of it is correct.  By the time you've melted the salt you've applied enough heat to provide the activation energy required for the sodium break free from the chlorine and react with things that it likes more than chlorine, like the hydroxyls in water.

The bonding energy of NaOH (sodium + hydroxyl (OH)) is lower than the bonding energy of NaCl (sodium + chlorine -- salt), so the reaction is exothermic.

Anyone interested in exploring the topic further can google the terms in bold.  It's pretty cool stuff. Also highly relevant: properties of alkali metals.

[NuclearNut]

 The water hammer effect strikes again.  As stated above this molten NaCl salt (which I am assuming it is, rather than some fluoride salt or something like that) it will be reacting with the water chemically and in a quite exothermic manner as well as heating the water to an extreme degree, causing it to expand in a steam explosion.  Because the water that is not a gas is incompressible to a great degree it ends up smashing the glass like a solid rock propelled by a similar explosion.

[lajoswinkler]

Unless you really know what's going on here, you shouldn't be saying something definitively occurs.

 

This is not and can not be a chemical reaction. Sodium chloride will not react with water. Any notion that it decomposes into sodium is absurd.

Also, even if it's extremely hot, it would push the hydrogen+oxygen<->water balance towards left, but that would not cause anything and it would be same as if you used just about anything inert and very hot. It's a physical reaction. Salt solidifies on the surface, then shatters. Water breaks in. Again, layer solidifies, shatters. It creates a lot of surface area and water flash boils.

 

Because this is all in a large breakable tub of water, it's easy for the detonation to shatter it into pieces.

[StrandedonEarth]

Full Video:

I'll admit that I hadn't actually watched the first video until just now, as I was on mobile. So my previous post was just based on the comments in the thread. Now having watched the video, that is certainly impressive, and it's certainly the incompressibility of water that breaks the glass. It's interesting to note that he didn't get the boom until he heated the salt well past the meltng point. He also didn't get a boom from the other ionic liquids he tried, but I wonder if he had also super-heated those. Finally, he decides the boom was from a physical reaction, not a chemical reaction, by testing the pH before and after and finding it still neutral. I have to wonder if he used super-heated salt for the pH experiment.

[StrandedonEarth]

22 hours ago, Tex_NL said:

If you want a BIG boom you throw a cup of water in a pot of boiling oil over an open flame.

This one time (resist urge to say "at band camp" - failed) I accidentally lowered a basket of dripping wet french fries into hot lard, which generated a cloud of oil droplets, which then flashed into a fireball when the cloud reached the burner. mpressively scary.