This is an oldie but goodie for demonstrating how increased surface area leads to increased rate of reactions.
Materials: flour large coffee can with lid or ice cream tub with lid candle 3 ft of tubing small plastic or metal can (prescription bottle or tomato juice can) bunsen burner spatula or spoon
Set Up: Run the tubing thru the side near the bottom of the large can and to the side near the bottom of the small can. The small can should be upright and in the middle of the the large can. The diameter of the tubing should be large enough so that when the small can is half full of flour it can be finely dispersed by blowing vigorously into the end of the tubing.
Procedure: Demonstrate with flour on a spoon and a bunsen burner that flour is not very flammable under normal conditions. When finely dispersed the reaction goes much faster. Light the candle. Put the lid on the large can and blow long and hard into the tubing. You will get a nice "whump" and the lid will blow off and about 6" to 1' of flame will shoot out of the large can for an instant. There will be a slight smell of burnt protein and a little flour dust on the table but no large mess. As always you will want to have safety glasses on and an extinguisher nearby. Variations: wood dust, powdered coal (could be very powerful. Be careful.)
Mark E Lockhart