Baking soda is sodium bicarbonate, NaHCO₃. That dissolves in water to become Na+ plus HCO₃-. In the presence of acid, H+, the bicarbonate ion combines with the acid protons to become hydrogen carbonate or carbonic acid, H₂CO₃. H₂CO₃ has a tendency to dissociate into carbon dioxide, CO₂, and water, H₂O. CO₂ can then come out of solution, becoming carbon dioxide gas, which forms bubbles, thereby causing the bread to rise.

Baking soda is sodium bicarbonate (a chemically basic compound). When baking soda is mixed with moisture and an acidic ingredient (e.g., yogurt, chocolate, buttermilk, and honey), the resulting chemical reaction produces bubbles of carbon dioxide that expand when cooking in the oven, causing baked goods to rise. This reaction happens immediately upon mixing ingredients, so you need to bake quickly after mixing for maximum rise.Baking powder is sodium bicarbonate, mixed with an acidifying agent (cream of tarter) and a drying agent (starch). It releases carbon dioxide when moist. They are somewhat interchangeable in recipes - but they have different taste - baking soda needs an acid to react and to balance out the bitter, basic taste, whereas baking powder has a more neutral taste (since it already contains an acid and a base). Baking soda won't work in recipes that call for baking powder and have no acidic ingredient (e.g. some cakes).