I loved this article from Epicurious: Baking Soda Vs. Baking Powder.
My first ever kitchen disaster happened in high school home economics. I made baking powder biscuits. Um, actually they turned out to be baking soda biscuits by mistake. What came out of the oven was black and inedible. I was completely shocked that a little bit of white powder could make such a dramatic difference. Thank goodness for classmates who shared their tasty treats! It was a lesson I'll never forget, and a reminder that baking is just as much a science as an art.
Not only does this article explain the chemical difference between baking soda and baking powder, but it gives some fantastic advice for those who like to tinker with recipes. If you plan to play around with some improv in your baking, this article is a must-read!