carbon dioxide

it is prodeced when



baking soda + vinegar = carbon dioxide

acetic acid (makes vinegar sour) + sodium bicarbonate (compound in baking soda) = carbonic acid.
It's really a double replacement reaction.

Carbonic acid is unstable, and it immediately falls apart into carbon dioxide and water (it's a decomposition reaction). The bubbles you see from the reaction come from the carbon dioxide escaping the solution that is left.

 Carbon dioxide is heavier than air, so, it flows almost like water when it overflows the container. It is a gas that you exhale (though in small amounts), because it is a product of the reactions that keep your body going.