Animated Solution for Chemistry - s and p-Block Elements: Reaction of ammonia with excess ${\text{Cl}}_2$ gives

The reaction between ammonia ($N{H}_3$) and chlorine ($C{l}_2$) is a classic and highly tested concept in p-block chemistry. What makes this reaction so fascinating is that the products completely change depending on which reactant is present in excess. It is a perfect example of how stoichiometry and limiting reagents can dictate the chemical pathway.

In this specific problem, we are given that chlorine ($C{l}_2$) is in excess.

To understand what happens, we need to look at the chemical personality of chlorine. Chlorine is a powerful oxidizing and halogenating agent. When it is abundant, it does not just react mildly; it aggressively attacks the ammonia molecule. Its primary goal is to replace the hydrogen atoms attached to the nitrogen.

Because chlorine is in excess, it will continue to substitute the hydrogen atoms until there are none left. One molecule of ammonia will react with three molecules of chlorine.

The three hydrogen atoms from ammonia combine with three chlorine atoms to form three molecules of hydrogen chloride ($HCl$). The remaining three chlorine atoms attach themselves to the nitrogen atom, forming nitrogen trichloride ($NC{l}_3$).

The balanced chemical equation for this process is:

Nitrogen trichloride ($NC{l}_3$) is a highly unstable, yellow, explosive liquid. It is a dangerous compound that must be handled with extreme care in the laboratory.

From our balanced equation, it is crystal clear that the products formed are nitrogen trichloride ($NC{l}_3$) and hydrogen chloride ($HCl$).

When we match these products with the given options, we find that option (d) perfectly aligns with our derived result.

The Reverse Scenario

What if the situation was reversed? What if ammonia ($N{H}_3$) was in excess instead of chlorine? This is a favorite twist in JEE and NEET exams.

In that scenario, ammonia acts as a reducing agent. It reduces chlorine to chloride ions while oxidizing itself to nitrogen gas ($N_2$). The initial reaction produces $N_2$ and $HCl$. However, because ammonia is a base and is present in excess, it immediately reacts with the acidic $HCl$ to form a salt, ammonium chloride ($N{H}_{4}Cl$).

The overall balanced equation for the excess ammonia scenario is:

This reaction is characterized by the formation of dense white fumes of ammonium chloride. Always pay close attention to the word "excess" in these types of problems, as it completely alters the chemical destiny of the reactants!