When you add an acid to a base, you form a weaker acid and a weaker base, releasing energy.
Example: Sulfuric acid + water -> Hydronium ion + sulfate ion
Sulfuric acid = stronger acid
water = stronger base
hydronium ion = weaker acid
sulfate ion = weaker base
High energy reactants to the left, lower energy products to the right
The released energy is heat
When you add the right amount of water to an acid, you can heat the acid-water interface, releasing enough heat around that boundary to boil the water, which rapidly expands into a gas, making the acid shoot out from the container due to the volume increase