They may appear a bit mysterious but actually they’re components of the same category. Both are known as “chemical leaveners.”
The most simplistic way to examine these two substances is to first understand what they have in common.
The goal of both is to release carbon dioxide gas which enables baked goods to rise. Both need moisture and heat is not required to initiate the release. It is highly recommended that products be placed in the oven immediately after the mixing process.
Baking Soda is alkaline. In order to produce the necessary carbon dioxide, an acid such as buttermilk or citrus must be added.
Baking Powder is acidic. It contains one or more acids such as cream of tarter and/or sodium aluminum sulfate.
Single-Acting Baking Powder releases gas immediately. Move products directly to the oven or risk losing some much needed gas bubbles.
Double-Acting Baking Powder is more forgiving. The substance releases a small burst of gas when moisture is introduced and a second burst when heat is applied. Therefore, double-acting is the more popular choice for enthusiastic bakers.