The reason for that is because vinegar and baking soda react to produce carbon dioxide. Now we know that a gas occupies as much volume as is available to it. So the carbon dioxide produced occupies the space in the balloon. When more gas is produced, it exerts pressure on the sides of the balloon. Since balloons are stretchable, they expand as the amount of gas increases. They keep on expanding as more gas is produced and we witness this as the balloon blows up.
Now, why do vinegar and baking soda give off carbon dioxide. Actually, vinegar is a solution of acetic acid. Baking soda, in chemical terms, is sodium bicarbonate. Now when they react, the following reaction occurs:
NaHCO3 (aq) + CH3COOH (aq) ----> CO2 (g) + H2O (l) + CH3COONa (aq)
This is an acid base reaction.
Now, why do vinegar and baking soda give off carbon dioxide. Actually, vinegar is a solution of acetic acid. Baking soda, in chemical terms, is sodium bicarbonate. Now when they react, the following reaction occurs:
NaHCO3 (aq) + CH3COOH (aq) ----> CO2 (g) + H2O (l) + CH3COONa (aq)
This is an acid base reaction.