Spoiler alert: They are not interchangeable
You’ve definitely come across baking soda and baking powder, two ingredients that sound similar but do very different things. Maybe you’ve started making a batter from scratch (for a cookie, pancake, cake, what have you) and realize that you have baking powder when it asks for baking soda, so you figure that you can substitute baking powder for baking soda. And then you learn the hard way because they are not interchangeable. If you swap baking powder for baking soda when making cookies, they become cake-y. Similarly, if you swap soda for powder when making pancakes, they won’t rise properly and will come out overcooked and dense.
So what’s the difference between baking soda and baking powder? It all comes down to science. Baking soda reacts to acids (like buttermilk, yogurt, chocolate, lemon juice, maple syrup, molasses, sour cream, applesauce, or honey) and causes a fast leavening reaction that results in spreading rather than rising. Baking powder is made up of baking soda plus an acid-based additive like cream of tartar or cornstarch, which creates a longer-lasting reaction when heat and/or liquid is added. The good news is if you have baking soda, you can make your own baking powder at home so you’ll never make this common baking error again.