Sparky
Cannabis use as medicine
Hope!
A good topic is whatever YOU find interesting! For myself, I like something practical.. something that people can use in their real lives.. for eg. why metal oxizides - people will remember this and not leave their tools out in the rain :-)
How about how substance abuse affects your body? How do chemicals in our brains, create moods? Or understanding pheromones?
Since 'climate change' is now a hot topic, you could be a little controversial and talk about the grand solar minimum - how chemical changes in the sun are really what are effecting the weather..
hope this helps..