Why do cupcakes rise when you put them in the oven?

Cupcakes rise in the oven primarily due to the production of gases from the leavening agents, such as baking powder or baking soda, which react with moisture and heat. As the batter heats up, the gases expand, creating air pockets that cause the cupcake to rise. Additionally, the moisture in the batter turns to steam, further contributing to the rise. The structure of the batter sets as it bakes, resulting in a light and fluffy texture.