According to Steve Spangler Science, mixing vinegar and baking soda starts a chemical reaction that produces carbon dioxide, or CO2, and water. The chemical names of the two ingredients are acetic acid, which is the vinegar, and sodium bicarbonate, which is the baking soda.
When vinegar and baking soda is mixed in a lunch bag or similar container, the carbon dioxide produced fills up the container. The container bursts or “explodes” when there is no more space for the gas in the bag or container.
In Scientific American’s version of the experiment, a film canister gets launched into the atmosphere like a rocket. The gas builds up in the canister until the lack of room pressurizes the closed canister causing it to pop open and fly into the air.