The following is a list of dangerous chemicals that should be generally avoided. Mixing these chemicals together causes violent reactions ranging from spontaneous fires to explosions. If you are properly trained, these may be good demonstrations to show your students. If you are not properly trained you should be very careful that you do not accidently create an energetic device -- as some of these ingredients have been known to be used in creating energetics and fuses for such things.
(1) Potassium Permanganate & Antifreeze --> spontaneous chemical fire
(2) Potassium Permanganate & Glycerine --> spontaneous chemical fire
*Potassium permanganate may be found in first aid kits in which it can be used as an mild antiseptic for relief.
(3) Iron Oxide (Rust) & Aluminum powder --> thermite (can burn through steel)
If you mix these two powders together and ignite the mixture with a high-heat source (such as a sparkler firework) it creates thermite which gets very hot and can burn through an engine block.
(4) Styrofoam & acetone --> improvised napalm
Styrofoam will melt in acetone (nail polish) and the resulting thick gooey stuff, if say soaked in kerosine and lit will create a compound that has an affect similar to napalm. Very dangerous, be sure to never do this unless you have the proper equipment and permits.
(5) Potassium chlorate & sugar --> rocket propellent
This is an extremely dangerous combination. It is sensitive to movement, and dropping this combination or mixture could result in an explosion.
Remember anytime a propellent is confined the pressure will build up and explode the container that confines it. For this reason, it has to be reiterated that the above information is for information purposes only. Be safe!
(6) Never mix chlorine bleach with ammonia as this creates a toxic gas. But never ever ever mix the more concentrated chlorine tablets with ammonia as this creates an even more concentrated gas. This gas has been known to be able to repel large animals from an area (say your home).
(7) Pyromaniacs have been known to add the styrofoam & acetone mixture from (4) to bottles, fill it with kerosine & oil, plug it leaving a length of soaked cloth protruding from the bottle. This has been a devistating "Malcolm X cocktail" which should be avoided at all costs because of its long-lasting and hot burning properties. This might be an interesting experiment to do in an open field on a rainy day on an old abandoned vehicle.