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) NCl₃ and HCl.

Step 1: Identify the Reactants

In this question, the reactants are ammonia (NH₃) and excess chlorine (Cl₂). Excess chlorine indicates there is more chlorine available than is necessary to react with the available ammonia.

Step 2: Analyze Potential Products

When ammonia reacts with chlorine, multiple reactions may occur depending on the relative concentrations. Since chlorine is in excess, it is likely that chlorine will oxidize ammonia more completely, leading us to expected products like nitrogen gas (N₂) or possibly nitrogen trichloride (NCl₃) along with hydrochloric acid (HCl).

Step 3: Write Balanced Chemical Equation

One potential balanced equation for an excess of chlorine reacting with ammonia is: 3NH₃ + 3Cl₂ → NCl₃ + 3HCl This equation suggests that nitrogen trichloride and hydrochloric acid are formed. Another less likely reaction due to conditions is where nitrogen gas, N₂ and HCl are formed, but the presence of excess chlorine and specific conditions will favor the formation of NCl₃.

Step 4: Consider Mechanisms and Side Reactions

Excess chlorine often leads to the formation of NCl₃ rather than solely N₂, particularly because NCl₃ is a product when ammonia is over-chlorinated. Hydrochloric acid is also a typical side product due to the excess chlorine. Therefore, we expect either N₂ and HCl or NCl₃ and HCl in conditions of excess chlorine over ammonia.

Step 5: Match with Given Options

Looking at the options, (c) NCl₃ and HCl matches the expected products when ammonia reacts with excess chlorine in this common industrial scenario.

Key Concepts

Chemical Reaction Products

When chemicals react, they transform into different substances called products. In the reaction of ammonia with chlorine, the products formed can vary based on the amount of chlorine available. If ammonia (\( \text{NH}_3 \)) is reacted with an excess of chlorine (\( \text{Cl}_2 \)), the chemical reaction tends to produce nitrogen trichloride (\( \text{NCl}_3 \)) and hydrochloric acid (\( \text{HCl} \)). This is mainly because chlorine, being in excess, completely reacts with the available ammonia.

• Nitrogen trichloride is a yellow oily liquid known for being very explosive.
• Hydrochloric acid is widely used in the chemical industry as a strong acid.

These products suggest a complete oxidation and chlorination reaction, which occurs commonly when ammonia is exposed to more chlorine than it can fully react with to form simpler products like nitrogen gas. Understanding reaction products helps us predict outcomes in a chemical process and informs industrial applications.

Excess Reactants in Chemical Reactions

In chemical reactions, the term "excess reactant" refers to the substance that is present in a greater quantity than necessary for the complete reaction with the limiting reactant. Here, when ammonia reacts with chlorine, the chlorine is in excess. This means there is more chlorine available than is required to completely react with all the ammonia.
Excess chlorine changes the typical dynamics of the reaction:

• It ensures that all ammonia reacts, increasing the potential yield of products like \( \text{NCl}_3 \) and \( \text{HCl} \).
• Leads to over-chlorination which favors different by-products than when reactants are in a balanced ratio.
• May introduce side reactions, contributing different compounds as minor products.

Understanding excess reactants helps in controlling chemical reactions, optimizing product yield, and predicting unexpected products that may form under certain conditions.

Balanced Chemical Equations

A balanced chemical equation ensures that the number of atoms for each element is equal on both sides of the equation. This reflects the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction. For the reaction of ammonia and chlorine, a balanced equation could look like this:\[3\text{NH}_3 + 3\text{Cl}_2 \rightarrow \text{NCl}_3 + 3\text{HCl}\]

• Each element (nitrogen, hydrogen, and chlorine) has the same number of atoms on both sides of the equation.
• The coefficients must be adjusted to achieve this balance.
• Balancing ensures the chemical equation correctly represents the stoichiometry of the reaction, guiding how much of each reactant will be required for the desired amount of products.

Grasping balanced equations is crucial for understanding precise chemical reactions and managing resources in chemical engineering and research scenarios.

Ammonia Oxidation

Ammonia oxidation involves the process where ammonia (\( \text{NH}_3 \)) loses electrons due to a chemical reaction and forms products such as nitrogen gas or nitrogen compounds. In the presence of excess chlorine, ammonia is oxidized, but with an interesting twist in product formation resulting in nitrogen trichloride rather than typical nitrogen gas.

• This reaction is an example of over-chlorination, where more chlorine leads to the formation of nitrogen trichloride (\( \text{NCl}_3 \)).
• Less severe oxidation might typically result in nitrogen gas (\( \text{N}_2 \)), but the presence of excess chlorine influences the pathway.
• Ammonia oxidation varies based on conditions such as temperature, pressure, and the reactants' concentration.

By understanding ammonia oxidation, we can predict reaction pathways and outcomes which are essential for processes in agriculture, the production of explosives, or industrial synthesizing of chemicals.