Thermite Reaction - Smash! Bang! Boom!

There's so much science hanging here in this remarkably simple-to-perform demonstration.

Steve Spangler - former elementary science teacher - her explains that the kinetic energy from the ball bearing's banging together turn into thermal energy - enough to burn holes in the piece of construction paper. He then goes on to show the far cooler - to me, anyway - reaction of iron oxide (the rust on the outside of the ball bearings) and aluminum. Most folks - if they know that reaction - know it as thermite (check a few thermite reactions here).

Typically, though, the thermite reaction involves mixing aluminum and iron (III) oxide powders in a flower pot or some ceramic vessel. The reaction is then started with a separate reaction (it has high activation energy) and then produces molten iron and a huge pile of sparks. It's outstanding to watch FROM A DISTANCE. That whole FROM A DISTANCE and the need for some second reaction means that thermite is typically reserved for high school and college chemistry classes.

Spangler - who didn't come up with the idea, by the way - brings the reaction into far more manageable form by taking a rusty ball bearing (covered in iron oxide) right up against one covered in aluminum foil. Same reactants...good energy to start the reaction (from the KE of the ball bearings)...great sparks.

Yeah, it takes a little practice to get the technique down right, but it's way safer than the big thermite reaction that throws molten iron all over the place. Plus, you get to clean up the rusty ball bearing in the process.

Al _(s) + Fe₃O_{4 (s)} --> Al₂O_{3 (s)} + Fe _{(s or l)}

We can look at this for...

• activity series - aluminum more active than iron, so oxygen goes to aluminum
• energy transfer - kinetic energy becomes thermal energy becomes chemical energy becomes light and heat energy again
• corrosion - We're un-corroding the iron in favor of the aluminum.
• electrochemistry - electrons are leaving the aluminum (so it's the anode) and going to the iron (so it's the cathode)

I am so happy that I just got myself a pair of these rusty ball bearings myself.

First day of awesome AP chemistry, here we come.



Update: If you're looking to buy yourself a set of these, Flinn Scientific offers a slightly larger version of these rusty steel balls (AP 6256) for (as of April, 2013, anyway) $26.60. Plus you get a couple of sheets of aluminum foil, which are easily worth like a thousand dollars or something. They also have a video on their site (that I can't figure out how to embed here)