The reaction of ammonium carbonate decomposing into water, ammonia, and carbon dioxide is a decomposition reaction.

Here's why:

* Decomposition reaction: A single reactant breaks down into two or more products.

* In this case: Ammonium carbonate (NH₄)₂CO₃ is the single reactant, and it breaks down into water (H₂O), ammonia (NH₃), and carbon dioxide (CO₂).

The chemical equation for this reaction is:

(NH₄)₂CO₃ → H₂O + 2NH₃ + CO₂