The chemical equation you're looking for is incorrect. Sodium hydrogen carbonate (baking soda) does not break down into sodium carbon dioxide and water vapor.

Here's the correct breakdown of sodium hydrogen carbonate (NaHCO₃):

2 NaHCO₃ → Na₂CO₃ + H₂O + CO₂

This means that when heated, two molecules of sodium bicarbonate decompose to form:

* Sodium carbonate (Na₂CO₃)

* Water (H₂O)

* Carbon dioxide (CO₂) gas

Important Note: There is no such thing as "sodium carbon dioxide".