Here are two of my favorite reactions that my students absolutely love. 

This first one is the Combustion of a Gummi Bear.  To combust anything you need oxygen gas and the more oxygen gas you have, the bigger and badder the fire.  In this reaction we decompose molten potassium chlorate into potassium chloride and oxygen gas.  Then the sugar in the gummi bear combusts in an exothermic reaction producing an awesome fire.   The gummi bear itself acts as a catalyst so at the end of the reaction you’ll just have a test tube full of white salt (potassium chloride) and a gummi bear with no sugar (who’s been through a traumatic experience).  You’ll also see the flame is a lilac purple color due to the potassium ions present.

2 KClO3 (l) –> 2 KCl (s) + O2 (g)

C6H12O6 (s) + 6 O2 (g) –> 6 CO2 (g) + 6 H2O (g)

This second reaction is my favorite representation of a single replacement reaction or a spontaneous redox reaction.  It is where zinc metal is combined with a strong acid to produce hydrogen gas.  We can also see the ideal gas law in action when we keep producing moles of gas the volume of the balloon increases proportionally.  Lastly, this shows why we don’t use hydrogen gas for birthday parties (and how Mr. A. burns off the hair on his hand at least once a year).

Zn (s) + 2 H+ (aq) –> Zn+2 (aq) + H2 (g)