Sodium bicarbonate (NaHCO3) and water (H2O) are formed when anhydrous sodium carbonate (Na2CO3) reacts with hydrochloric acid (HCl) according to the following chemical reaction:

Na2CO3 + 2HCl → 2NaHCO3 + H2O

In this reaction, the sodium ions (Na+) from sodium carbonate combine with the chloride ions (Cl-) from hydrochloric acid to form sodium chloride (NaCl). The carbonate ions (CO32-) from sodium carbonate react with the hydrogen ions (H+) from hydrochloric acid to form carbonic acid (H2CO3), which quickly decomposes into water and carbon dioxide (CO2). The net result of the reaction is the formation of sodium bicarbonate and water.