Question

Ammonia reacts with excess of chlorine to form:
(A) ${N_2} + N{H_4}Cl$
(B) $NC{l_3}{\text{ }}and{\text{ }}HCl$
(C) $N{H_4}Cl{\text{ }}and{\text{ }}NC{l_3}$
(D) ${N_2}{\text{ }}and{\text{ }}HCl$

Answer 1

The reaction between Ammonia $\left( {N{H_3}} \right)$ and chlorine $\left( {C{l_2}} \right)$ can occur in two ways. That is either the excess amount of ammonia would react with the chlorine or these could be excess amounts of chlorine that could react with ammonia. In both these ways, the reaction involved would be a redox reaction, however the products would be different.

Complete step by step answer:
Ammonia $\left( {N{H_3}} \right)$ is a colourless gas that has a characteristic pungent smell. It can be easily liquified due to the presence of hydrogen bonding. $N{H_3}$ is lighter than air whereas chlorine is a yellow green gas at the room temperature and is a strong oxidizing agent.
The reaction between ammonia and chlorine, when the chlorine is present in excess amounts is a redox reaction and nitrogen trichloride and hydrogen chloride are produced as the products. The reaction can be written as:

$2N{H_3}\left( {ammonia} \right) + 3C{l_2}\left( {chlorine} \right) \to 2NC{l_3}\left( {nitrogen{\text{ }}trichloride} \right) + 6HCl\left( {hydrogen{\text{ }}chloride} \right)$

As we know that, in redox reactions, both the processes of oxidation and reduction do occur simultaneously and the electrons are being shared between the two species. So, here also the chlorine is reduced while the nitrogen atom of ammonia is oxidized as hydrogen atoms are being removed from it. Thus, this reaction is called a redox reaction, but, however the oxidation number of nitrogen remains the same and the oxidation state of chlorine changes from zero to $- 1$ and $+ 1$.
The product, nitrogen trichloride $\left( {NC{l_3}} \right)$ is a yellow pungent smelling liquid which is highly explosive in nature. This is due to the electronegativity difference. The electronegativity difference between $N$ and $Cl$ is lost and thus the bond between them is weaker and the compound is less stable and thus is highly explosive in nature. The other product which is hydrogen chloride $\left( {HCl} \right)$, is a colourless gas.
Hence, the answer is option (B).

Note:
The speed of the reaction between ammonia and chlorine increases with the increase in the concentration of nitrogen chloride and with the rise in temperature.