Baking Powder and Baking Soda....what's the difference?

Both of these raising agents contain a carbonate (Sodium Bicarbonate) which behaves in a predictable way when reacted with an ACID.

The general reaction
ACID + CARBONATE ----> METAL SALT + WATER + CARBON DIOXIDE.

It is the carbon dioxide gas that produces bubbles of air that makes the mixture rise. Click on this link to find out more.