Why do the balloon stop blowing up after baking soda and vinegar are combined?

When baking soda (sodium bicarbonate) and vinegar (acetic acid) are combined, they undergo a chemical reaction to form carbon dioxide gas, water, and sodium acetate. The carbon dioxide gas is what causes the balloon to inflate. However, the reaction will eventually stop when one of the reactants is used up. In this case, the limiting reactant is usually the baking soda, which is present in a smaller amount than the vinegar. Once all of the baking soda has been consumed, the reaction will stop and the balloon will stop inflating.