Problem 54 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The compound(s) which generate(s) \(\mathrm{N}_{2}\) gas upon thermal decomposition below \(300^{\circ} \mathrm{C}\) is (are)(a) \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) (b) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (c) \(\mathrm{Ba}\left(\mathrm{N}_{3}\right)_{2}\) (d) \(\mathrm{Mg}_{3} \mathrm{~N}_{2}\)

Step-by-Step Solution

Answer

Options (a), (b), and (c) generate \( \mathrm{N}_{2} \) gas below \( 300^{\circ} \mathrm{C} \).

Step 1: Analyze option a

The compound is ammonium nitrate, \( \mathrm{NH}_{4} \mathrm{NO}_{3} \). Upon thermal decomposition, this compound primarily produces \( \mathrm{N}_{2} \) gas along with water vapor and oxygen. This reaction occurs below \( 300^{\circ} \mathrm{C} \). Hence, this option is correct.

Step 2: Analyze option b

The compound is ammonium dichromate, \( (\mathrm{NH}_{4})_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} \). This also decomposes upon heating to produce \( \mathrm{N}_{2} \) gas, along with chromium(III) oxide and water. The decomposition occurs below \( 300^{\circ} \mathrm{C} \). Thus, this is also correct.

Step 3: Analyze option c

The compound is barium azide, \( \mathrm{Ba} \left(\mathrm{N}_{3}\right)_{2} \). When heated, barium azide decomposes to produce \( \mathrm{N}_{2} \) gas and barium metal. This decomposition reaction occurs below \( 300^{\circ} \mathrm{C} \). Therefore, this is another correct option.

Step 4: Analyze option d

The compound is magnesium nitride, \( \mathrm{Mg}_{3} \mathrm{N}_{2} \). This compound does not decompose to release \( \mathrm{N}_{2} \) upon heating. Instead, it reacts with water to produce ammonia. Thus, this option is not correct.

Key Concepts

Ammonium Nitrate

Ammonium nitrate, or \( \mathrm{NH}_{4}\mathrm{NO}_{3} \), is a chemical compound known for its role in fertilizers and explosives. This compound undergoes a fascinating process called thermal decomposition when it is heated. During this process, ammonium nitrate breaks down below \( 300^{\circ} \mathrm{C} \), releasing nitrogen gas \( \mathrm{N}_{2} \), water vapor, and oxygen. The decomposition can be represented by the chemical equation:\[\mathrm{NH}_{4} \mathrm{NO}_{3} \rightarrow \mathrm{N}_{2} + 2\mathrm{H}_{2}\mathrm{O} + \frac{1}{2} \mathrm{O}_{2} \]This makes ammonium nitrate a crucial compound in applications where a quick release of gases is needed, such as in airbags and some types of fireworks. The safety and efficacy of ammonium nitrate depend heavily on understanding its decomposition properties.

Ammonium Dichromate

Ammonium dichromate, known by the chemical formula \( (\mathrm{NH}_{4})_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} \), is recognized for its striking orange color and use in educational demonstrations of chemical volcanoes. Upon heating, this compound undergoes thermal decomposition below \( 300^{\circ} \mathrm{C} \), resulting in the formation of nitrogen gas \( \mathrm{N}_{2} \), chromium(III) oxide, and water vapor. The reaction is exothermic, releasing significant energy, and can be summarized by:\[ (\mathrm{NH}_{4})_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} \rightarrow \mathrm{Cr}_{2} \mathrm{O}_{3} + \mathrm{N}_{2} + 4 \mathrm{H}_{2} \mathrm{O} \]This reaction not only showcases thermal decomposition but also demonstrates the formation of solid chromium(III) oxide, contributing to an exciting visual effect where green ash is produced as a residue.

Barium Azide

Barium azide \( \mathrm{Ba}(\mathrm{N}_{3})_{2} \) is primarily used in detonators and tracer bullets due to its explosive properties upon decomposition. When heated, it decomposes at temperatures below \( 300^{\circ} \mathrm{C} \), releasing nitrogen gas \( \mathrm{N}_{2} \) and leaving behind pure barium metal. The decomposition can be represented by:\[ \mathrm{Ba}(\mathrm{N}_{3})_{2} \rightarrow \mathrm{Ba} + 3 \mathrm{N}_{2} \]Barium azide's ability to release gas so readily makes it suitable for applications that require rapid gas evolution. However, it's important to handle it with care due to its volatility.

Nitrogen Gas Evolution

Nitrogen gas evolution is a significant aspect of the thermal decomposition of various compounds, including ammonium nitrate, ammonium dichromate, and barium azide. When these compounds decompose, they release \( \mathrm{N}_{2} \) gas, which is an inert and colorless gas making up the largest portion of Earth's atmosphere. The evolution of nitrogen gas not only plays a crucial role in chemical reactions but also finds utility in various industries.

• In the automotive industry, evolved nitrogen gas is used in airbags.
• In pharmaceuticals, it is used to create inert environments.
• In food packaging, it helps preserve freshness by displacing oxygen.

Understanding how nitrogen gas is evolved from these compounds can help in designing safer and more efficient chemical processes, as well as in reducing environmental impact.