Baking powder is a leavening agent that is added to baked goods before cooking to help them rise.
How Is Baking Powder Different From Baking Soda?
Baking powder contains contains sodium bicarbonate (baking soda), but it also includes the acidifying agent (cream of tartar), and typically a starch as a drying agent.
You can find baking powder as single-acting and double-acting. Single-acting baking powder is activated by moisture, so if you use this type, you must bake immediately after adding it. Double-acting baking powders, like the name suggests, react in two phases. Because of this, they can set before baking.