Question

Nitrogen is liberated by the thermal decomposition of only (a) \(\mathrm{NH}_{4} \mathrm{NO}_{2}\) (b) \(\mathrm{NaN}_{3}\) (c) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (d) all the three

Short answer

All three compounds liberate nitrogen gas on thermal decomposition.

Step-by-step solution

Understanding the Problem

The problem asks which of the given compounds liberates nitrogen gas (N_2) when decomposed thermally. We will need to analyze the decomposition reactions of the compounds.

Analyzing Compound NH_4NO_2

When ammonium nitrite NH_4NO_2 decomposes, it breaks down to form nitrogen gas and water: 2NH_4NO_2 ightarrow 2N_2 + 4H_2O. This means that NH_4NO_2 liberates nitrogen gas during thermal decomposition.

Analyzing Compound NaN_3

Sodium azide (NaN_3) decomposes on heating to produce sodium and nitrogen gas: 2NaN_3 ightarrow 2Na + 3N_2. So, NaN_3 also liberates nitrogen gas during its thermal decomposition.

Analyzing Compound (NH_4)_2Cr_2O_7

Ammonium dichromate ((NH_4)_2Cr_2O_7) decomposes thermally to give chromium(III) oxide, nitrogen gas, and water vapor: (NH_4)_2Cr_2O_7 ightarrow Cr_2O_3 + N_2 + 4H_2O. Thus, this compound also liberates nitrogen gas.

Conclusion

All three compounds NH_4NO_2, NaN_3, and (NH_4)_2Cr_2O_7 liberate nitrogen gas (N_2) when decomposed thermally.

Key concepts

Ammonium Nitrite Decomposition

Ammonium nitrite, represented chemically as \( \mathrm{NH}_4 \mathrm{NO}_2 \), is a compound that decomposes distinctly during thermal processes. This decomposition reaction is both straightforward and chemically interesting. When ammonium nitrite is heated, it breaks down into gaseous nitrogen \( \mathrm{N}_2 \) and water vapor according to the following reaction: \[ 2\mathrm{NH}_4\mathrm{NO}_2 \rightarrow 2\mathrm{N}_2 + 4\mathrm{H}_2\mathrm{O} \]. This indicates a simple transformation where each molecule of ammonium nitrite results in a molecule of nitrogen gas and two molecules of water. Understanding this chemical breakdown is crucial in the context of studying gas evolution from solid compounds. The ability of ammonium nitrite to generate nitrogen gas upon heating is particularly significant in applications that require a clean and simple method of gas generation. However, in practice, the stability of ammonium nitrite is a point of caution since it can decompose violently if not handled with care. It underscores the need for controlled conditions during its decomposition to harness nitrogen gas effectively.

Sodium Azide Decomposition

Sodium azide, expressed as \( \mathrm{NaN}_3 \), offers a fascinating look into thermal decomposition chemistry. When subjected to heat, sodium azide splits into its elemental constituents. The decomposition reaction is: \[ 2\mathrm{NaN}_3 \rightarrow 2\mathrm{Na} + 3\mathrm{N}_2 \]. This equation illustrates that two moles of sodium azide yield two moles of sodium metal and three moles of nitrogen gas. This decomposition is particularly striking because it results in the release of a significant amount of nitrogen gas while forming elemental sodium. This property of sodium azide finds practical applications in airbag systems, where a rapid deployment of nitrogen gas is essential for inflation. The reliable generation of nitrogen gas makes sodium azide valuable in industries that require safe and quick production of high volumes of \( \mathrm{N}_2 \). Despite its usefulness, sodium azide is handled with utmost caution due to its toxicity and potential explosive nature under improper conditions.

Ammonium Dichromate Decomposition

The decomposition of ammonium dichromate, \( (\mathrm{NH}_4)_2\mathrm{Cr}_2\mathrm{O}_7 \), is an intriguing reaction to explore. When heated, this compound undergoes a dramatic exothermic reaction that can be symbolized by the equation: \[ (\mathrm{NH}_4)_2\mathrm{Cr}_2\mathrm{O}_7 \rightarrow \mathrm{Cr}_2\mathrm{O}_3 + \mathrm{N}_2 + 4\mathrm{H}_2\mathrm{O} \]. The products of this reaction are chromium(III) oxide, nitrogen gas, and water vapor, marking a vivid transformation often used in demonstrations. This reaction is known as the "Volcano Reaction" due to its spectacular visual effect, emitting green chromium(III) oxide and releasing nitrogen gas in a fiery display. Students often encounter ammonium dichromate in laboratory settings, where it serves as a dramatic demonstration of chemical change. The liberation of nitrogen gas and the transformation into chromium(III) oxide emphasize critical skills in balancing chemical equations and understanding stoichiometry in decomposition reactions. It's crucial to manage the reaction environment carefully to ensure safety given the intensity of the exothermic process.