Hydrogen/Oxygen Balloons

Description

Three balloons are filled with gases. Two of the balloons rise to the ends of their strings, while the third hangs down. When a small flame is applied to the balloons:

- the hanging balloon goes POP!

- the second balloon goes BOOM!

- the third balloon goes BANG! (Really, really loudly!)

Explanation

First, whether a balloon rises or sinks in air depends on the density of the gas within it. One balloon contained oxygen gas (O₂), which is more dense than air. That balloon sank. A second balloon contained hydrogen gas (H₂), which is less dense than air, and it rose. The third balloon contained a mixture of H₂ and O₂. The mixture is also less dense than air, so it rose.

Densities:	air	1.29 g/L
	oxygen	1.43 g/L	sinks
	hydrogen	0.089 g/L	rises
	2:1 hydrogen + oxygen	0.536 g/L	rises

Second, hydrogen gas is combustible, that is, when a flame or spark is applied, it will react rapidly with oxygen to form water and produce heat and a flame. The reaction is so fast it creates an explosion.

2H₂(g) + O₂(g)2H₂O(l) + heat

Oxygen itself, contrary to popular belief, is not combustible! It's what other things react with when they combust. So when a flame was applied to the balloon containing only oxygen, it just popped.

When the flame was applied to the balloon containing only hydrogen, it combusted, but because it takes a little time for the hydrogen in the balloon to mix with the oxygen in the air before it can react, that combustion was relatively slow. It made a low-pitched boom.

Finally, when the balloon containing both hydrogen and oxygen was ignited, it exploded with a very loud bang! That's because when the hydrogen and oxygen are intimately mixed, the reaction happens much faster!

still have questions?  email us!

explanation furnished by UCCS's Dr. David Anderson

Site Map | Contact Us