I heard that if you put reservoir of liquid hydrogen on some gunpowder and light up the gunpowder then you won't get the shocking wave, but vacuum, because to burn down 50 liters of hydrogen at 10 bars will have to use about 1000 liters of oxygen and produce very little water.

Is it true or not?

liquid hydrohen?
may be a (as variant) nothing happen, because a hydrohen are freeze a steamed water and NITROGEN(N2) in air, and that is prevent to burn a gunpowder. but I may wrong.

quote:

Originally posted by hitko:
I heard that if you put reservoir of liquid hydrogen on some gunpowder and light up the gunpowder then you won't get the shocking wave, but vacuum, because to burn down 50 liters of hydrogen at 10 bars will have to use about 1000 liters of oxygen and produce very little water.

Is it true or not?

Not true. A 'vacuum bomb' is not possible.

First of all, air is only about 20% oxygen, so there is still 80% left of other gases even if all the oxygen disappeared. Let's suppose however that you surround the liquid hydrogen tank with pure oxygen.

The hydrogen will only burn where it is in contact with the oxygen. What happens therefore is not an explosion but a longer lasting fireball. Similar to the Hindenburg zeppelin disaster that the Mythbusters recreated in miniature. Let's suppose then that you instead blow up a container of pre-mixed oxygen and hydrogen gas.

The result of the reaction is indeed water, but when produced by this violent reaction it will be steam, i.e. gas. When cooled off, this will turn into water and crush any container it is in. In the open air it will not cool off quickly enough to give a vacuum/implosion effect.

An easier way to show this kind of thing at home is to skip the hydrogen/oxygen reaction and use steam directly. Get an empty coke can, put a small amount of water in it. Also get a bowl filled with ice water, an inch or more deep. Heat up the can on a stove until the water boils and the can gets filled with steam. Turn off the stove, then pick up the can (use oven gloves) and dunk it upside down in the ice water. The steam will suddenly condense, and this happens so quickly that the can is crushed rather than the ice water being sucked in.

Note that the can will not be crushed if you don't put the opening under water. However quickly the steam condenses, sucking in outside air is easy and the can will easily withstand that sucking pressure. Sucking in water is much harder, and the pressure needed for that is more than enough to crush the can.