What causes baking powder to react?

Baking powder reacts primarily due to its chemical components, which include an acid (usually cream of tartar) and a base (typically baking soda). When baking powder is moistened and exposed to heat, the acid and base react to produce carbon dioxide gas. This gas forms bubbles in the dough or batter, causing it to rise and become light and fluffy. The reaction is complete during baking, which is why it's important to bake the mixture soon after mixing for optimal leavening.