Here's a simple explanation:

* Carbonates are compounds containing the carbonate ion (CO3^2-).

* Acids contain hydrogen ions (H+).

* When carbonates react with acids, the hydrogen ions from the acid react with the carbonate ions, forming carbonic acid (H2CO3).

* Carbonic acid is unstable and quickly decomposes into carbon dioxide and water.

This reaction is often used to test for the presence of carbonates. The release of carbon dioxide can be observed as bubbles or effervescence.