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Chemistry In Pictures

Chemistry in Pictures: Goodbye flowerpot

by Craig Bettenhausen
November 11, 2021


Sparks and flame fly from a terra cotta flower pot, which is breaking.
Credit: Submitted by Matt Joyner

If everyone is careful with safety—goggles, lab coats, fire extinguishers, and a safe distance—the thermite reaction is a knockout chemistry demonstration. Matt Joyner, a biochemistry professor at Pepperdine University, treated his summer research students to a classic presentation of the effect. Iron oxide (rust) powder and aluminum powder are mixed in a terra cotta flowerpot, where the hole at the bottom has been plugged. A heavy iron ring stand holds the pot, and when a fuse of some kind reaches the mixture, well, the photo tells the tale.

All things being equal, oxygen would rather bind to aluminum than to iron, energetically speaking. So iron oxide and aluminum metal should react to form aluminum oxide and iron metal and release a lot of energy in the process, following this chemical reaction: 2Al + Fe2O3 → 2Fe + Al2O3. But the activation barrier for the oxygen to switch metals is high, so mixing the two together cold does nothing. A strip of magnesium, or sometimes a humble sparkler, burns hot enough to get things rolling and then sparks literally fly.

Submitted by Matt Joyner

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