1. Diffusion Rates:
* Ammonia (NH₃) is lighter than HCl: Ammonia gas has a lower molecular weight than hydrogen chloride. This means ammonia molecules move faster and diffuse more quickly through the air.
* HCl diffuses slower: HCl is heavier and diffuses more slowly.
2. The Reaction:
* Ammonia and HCl react in the air: When ammonia and HCl gas molecules collide, they react to form ammonium chloride (NH₄Cl). This reaction is exothermic (releases heat).
3. The Result:
* More collisions near the HCl end: Since HCl diffuses slower, it takes longer to spread out. This means there is a higher concentration of HCl molecules near the HCl end of the tube.
* More collisions mean more ammonium chloride: Because there's more HCl closer to the HCl end, more collisions occur, resulting in more ammonium chloride formation near that location.
In essence, the ammonium chloride forms closer to the HCl end because the HCl gas diffuses more slowly and therefore creates a denser cloud of HCl molecules for the ammonia to react with.
