What happens when baking soda and vinegar are combined?
When Baking soda and vinegar are combined, it makes a fizzing
reaction when the Acetic acid in the vinegar reacts with Sodium
Bicarbonate (the chemical name for baking soda).
The result is some water, Sodium Acetate and Carbon Dioxide gas
What actually happens is this: the acetic acid (that's what
makes vinegar sour) reacts with sodium bicarbonate (a compound
that's in baking soda) to form 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.
What's left is a dilute solution of sodium acetate in water.
Acetic Acid: CH3COOH -> CH3COO- + H+
Sodium Bicarbonate: NaHCO3 -> Na+ + HCO3 -
H++ HCO3- -> H2CO3 Carbonic Acid
H2CO3 -> H2O + CO2
It will "explode" in a way that most kids with those materials
to hand could tell you about.