Problem 77 - A Complete Resource Book in Chemistry for JEE Main

Question

What are the products obtained when ammonia is reacted with excess chlorine? (a) \(\mathrm{N}_{2}\) and \(\mathrm{NH}_{4} \mathrm{Cl}\) (b) \(\mathrm{N}_{2}\) and \(\mathrm{NCl}_{3}\) (c) \(\mathrm{NCl}_{3}\) and \(\mathrm{HCl}\) (d) \(\mathrm{N}_{2}\) and \(\mathrm{HCl}\)

Step-by-Step Solution

Answer

(c) \(\mathrm{NCl}_3\) and \(\mathrm{HCl}\)

Step 1: Understand the Chemical Reaction

When ammonia \((\mathrm{NH}_3)\) reacts with excess chlorine \((\mathrm{Cl}_2)\), two possible reactions can occur. With an excess of chlorine, the reaction tends to completely chlorinate ammonia, meaning all of the hydrogen atoms in ammonia are replaced by chlorine atoms.

Step 2: Write Down Possible Reactions

One possibility is the formation of nitrogen trichloride \((\mathrm{NCl}_3)\) and hydrochloric acid \((\mathrm{HCl})\). The balanced chemical equation for this reaction is:\[ \mathrm{NH}_3 + 3\mathrm{Cl}_2 \rightarrow \mathrm{NCl}_3 + 3\mathrm{HCl} \]

Step 3: Identify Reaction Type

This is an example of a substitution reaction where chlorine replaces hydrogen in ammonia. Since there is excess chlorine, the formation of \(\mathrm{NCl}_3\) and \(\mathrm{HCl}\) will be the major products.

Step 4: Verify the Conditions

Verify that chlorine is in excess. In this reaction, chlorine is indeed in excess, which favors the complete chloration of ammonia leading primarily to \(\mathrm{NCl}_3\) and \(\mathrm{HCl}\).

Key Concepts

Substitution Reaction

In chemistry, a substitution reaction is where one atom or a group of atoms in a molecule is replaced by another atom or group. This is a fundamental type of reaction that occurs in organic and inorganic chemistry alike.
Substitution reactions are common in many chemical processes. In these reactions, halogens often replace hydrogen atoms in hydrocarbons and other hydrogen-containing molecules. This process is usually guided by the reactivity of the substituting atom, as well as the conditions such as temperature and the presence of a catalyst.
For example, when we consider ammonia (\(\mathrm{NH}_3\)) reacting with chlorine (\(\mathrm{Cl}_2\)), this is a substitution reaction where chlorine atoms replace hydrogen atoms in ammonia.

Ammonia and Chlorine Reaction

When ammonia (\(\mathrm{NH}_3\)) reacts with chlorine (\(\mathrm{Cl}_2\)), there are various possible outcomes depending on the relative amounts of reactants. If chlorine is present in excess compared to ammonia, a specific reaction tends to predominate.

• In the presence of excess chlorine, a complete reaction occurs, transforming the ammonia entirely into nitrogen trichloride (\(\mathrm{NCl}_3\)) and hydrochloric acid (\(\mathrm{HCl}\)).
• The balanced chemical equation for this reaction is: \[ \mathrm{NH}_3 + 3\mathrm{Cl}_2 \rightarrow \mathrm{NCl}_3 + 3\mathrm{HCl} \]

This equation shows each ammonia molecule being converted into one nitrogen trichloride molecule, while each chlorine molecule turns into two hydrochloric acid molecules. This complete chlorination is a typical result when chlorine is used in excess.

Reaction Products

Understanding the reaction products is crucial in predicting the outcomes of chemical reactions. For the reaction between ammonia (\(\mathrm{NH}_3\)) and excess chlorine (\(\mathrm{Cl}_2\)), the major products formed are nitrogen trichloride (\(\mathrm{NCl}_3\)) and hydrochloric acid (\(\mathrm{HCl}\)).

• **Nitrogen Trichloride (\(\mathrm{NCl}_3\)):** It is a yellow, oily liquid with a sharp smell. Caution must be exercised with \(\mathrm{NCl}_3\) due to its explosiveness under certain conditions.


• **Hydrochloric Acid (\(\mathrm{HCl}\)):** In this reaction, it is a gaseous product that can dissolve in water to form a strong acid, commonly known for its use in industry and laboratory settings.

The formation of \(\mathrm{NCl}_3\) and \(\mathrm{HCl}\) in this substitution reaction highlights chlorine's role in replacing hydrogen atoms in ammonia under these conditions.