 |
| Thanks to my good friend and fellow science teacher, Josh, who makes the high speed videos. |
Who doesn’t love the thermite reaction? This reaction is exciting, dramatic, and a
bit scary. Shakhashiri describes it
like this, “Flame, flying sparks, smoke, and dust are produced. Molten iron runs through the hole in the pot
into the sand bath.” I pulled out this
demo today as part of the “5-types of chemical reactions” unit and a great
example of an exothermic reaction.
Thermite is a single displacement reaction with a high activation energy. The thermite mixture, aluminum powder and iron oxide, can sit on the shelf
quietly without much concern because it takes another reaction to get it
started.
 |
| Inserting the ignition stick into the thermite mixture. |
I tried to use the potassium permanganate reaction with
glycerin (as described by Shakhashiri) to get the reaction going. I did the potassium permanganate reaction
yesterday in class, so it seemed like a nice follow up today. (By the way, it filled up the room with smoke
and we all poured out of the classroom coughing as the bell rang at the end the
period. I’ll do it outside next time!) The
permanganate reacted vigorously with the glycerin, but it did not produce
enough heat to spark the thermite. (You
can watch this “dud” reaction at the end of the “Thermite Balls” video.)
 |
| Take a look at the chunk of iron that we collected from the water bath. |
 |
| A close-up of the iron drops that formed from the reaction. |
So I went back to the stand-by: thermite ignition sticks that we bought from
the chemical supply company. These
sticks are essentially really fat sparklers.
I used a Bunsen burner to light the stick, and then I ran outside with
my burning sparkler. I held it in the
thermite mixture until the reaction started.
Once it got going, all that was left to do was stand back and enjoy the
show. Watch for the molten iron dropping
out of the bottom of the clay pot, making the water in the tank boil. I fished out the iron pellet from the tank to
show the kids the iron drops that formed.
I followed up the thermite reaction with what I
call “hand held thermite” or “thermite balls”.
I can make the same reaction on a smaller scale with two rusty cannon
balls, one covered with aluminum foil.
With enough activation energy, provided by hitting the balls together at
a high speed, sparks fly and there’s a loud pop. The high speed video doesn’t do justice to
the reaction without the sound effects, but you get to see the classic facial
expressions I make when I do the demo. I
never realized how much I flip my hair until I started this blog project.
 |
| Ready for the hand held thermite reaction. |
