What happens when hydrogen gas is burned with a lit splint?

• A. It burns with a squeaky pop
• B. It burns with a loud explosion
• C. It glows red without flame
• D. It remains unreactive

Answer: (A)

Igniting hydrogen in air makes a squeaky pop because the flame causes the hot gases to expand very quickly and push on the surrounding air, sending a tiny shock wave that you hear as a sharp pop. The reaction is hydrogen and oxygen turning into water, releasing energy in a very short moment, and with only a small amount of gas the energy goes into a quick pressure pulse rather than a big blast. That’s why you don’t get a large explosion in this simple setup. A red glow isn’t seen here because hydrogen flames are not red; they’re pale blue and often nearly invisible in daylight. Hydrogen is reactive with oxygen when ignited, so it wouldn’t remain unreactive.