When we heat baking powder
2NaHCO3 forms Na2CO3+CO2+H2O
CO2 that is released makes cake or bread swells on adding baking powder.

Introduction:
Baking powder is a commonly used leavening agent in baking. It is a combination of baking soda, cream of tartar, and a moisture-absorbing agent. It is used in cakes, bread, and other baked goods to help them rise and become light and fluffy.

How does baking powder work?
Baking powder releases carbon dioxide gas when it comes into contact with moisture and heat. This gas causes the batter or dough to rise, resulting in a light and airy texture. Baking powder works in two stages:

Stage 1: When baking powder is added to the batter or dough, the moisture in the mixture activates the baking soda in the powder. This reaction produces carbon dioxide gas.

Stage 2: When the mixture is heated in the oven, the heat causes the remaining baking powder ingredients, cream of tartar and moisture-absorbing agent, to release more carbon dioxide gas. This gas causes the mixture to rise further, resulting in a fluffy texture.

Why does cake or bread swell on adding baking powder?
When baking powder is added to cake or bread batter, the carbon dioxide gas produced causes the batter to rise, resulting in a light and fluffy texture. The gas forms bubbles throughout the batter, which expand as the mixture is heated in the oven. The expansion of these bubbles causes the cake or bread to rise and swell.

Conclusion:
In conclusion, baking powder is a leavening agent that is commonly used in baking to help cakes, bread and other baked goods rise and become light and fluffy. It works by releasing carbon dioxide gas when it comes into contact with moisture and heat. This gas causes the batter or dough to rise, resulting in a light and airy texture.