Final answer:
The given reaction is a synthesis reaction, where ammonia, carbon dioxide, and water combine to form ammonium bicarbonate.
Step-by-step explanation:
The equation NH3 + CO2 + H2O → NH4HCO3 represents a synthesis reaction. In a synthesis reaction, two or more simple substances combine to form a more complex compound. Here, ammonia (NH3), carbon dioxide (CO2), and water (H2O) react to form ammonium bicarbonate (NH4HCO3), which is a single product consisting of the combined elements.