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Igniting H2 and O2 in a balloon

photo, flame from balloon explosion

Why does igniting a balloon filled with H2 produce a loud bang?

photo, green balloon

The balloon is filled with flammable hydrogen gas. We can tell that the balloon contains a gas that is less dense than air since the balloon appears to float above the surface.

 

A balloon filled with hydrogen gas burns when ignited but does not produce a large bang. If the balloon is filled with hydrogen and then allowed to remain untouched for a while, oxygen gas from the air begins to effuse through the tiny pores in the balloon. After a while, the balloon contains a mixture of H2, O2 and some other non-reactive gases.
small photo, green balloon

Video for Windows
small photo, green balloon

Quicktime

When ignited with a lighted candle, the gases inside the balloon quickly react to produce yellow flames and a large bang.

 

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