The presentation that I remember most were demonstrating the effect of surface area on reaction rate (a lesson I haven't forgotton!)
Cheesy and insignificant as it sounds, the teacher took some lycopodium powder..put it in a pile, and lit a match and put it on top. The powder kinda fizzled a tiny pit...but the flame got extinguished. Then he took some lycopodium powder in his hand, and held a lit match between his fingers. He jerked his hand upward so the powder would spread up and outwards, passing the match in transit (obviously with a greater surface area). The powder combusted into a short-lived ball of fire...like 2 feet tall and one foot wide. It was AMAZING!
I also remember when he took a particular crystal that could exist with or without a water of crystallization...He heated the hydrated one to dispell the water and it actually changed colour (neat eh? I know now that that's ligand chemistry
Anyways he had one guy put it in his hand, and then he put a tiny drop of water on it. The crystal readily recrystallized, and of course gave off some heat in the process...I remember the guy holding the reaction in his hand uttering an expletive lol...Heat of hydration is AWESOME (is that what its called)?