Problem 109 - A Complete Resource Book in Chemistry for JEE Main

Question

When \(\mathrm{AgNO}_{3}\) is heated strongly the products formed are (a) \(\mathrm{NO}\) and \(\mathrm{NO}_{2}\) (b) \(\mathrm{NO}_{2}\) and \(\mathrm{O}_{2}\) (c) \(\mathrm{NO}_{2}\) and \(\mathrm{N}_{2} \mathrm{O}\) (d) \(\mathrm{NO}\) and \(\mathrm{O}_{2}\)

Step-by-Step Solution

Answer

The correct answer is (b) \( \mathrm{NO}_{2} \) and \( \mathrm{O}_{2} \).

Step 1: Write the Chemical Reaction

When silver nitrate \( \text{AgNO}_{3} \) is heated, it decomposes into silver metal \( \text{Ag} \), nitrogen dioxide \( \text{NO}_{2} \), and oxygen gas \( \text{O}_{2} \). The balanced chemical equation is: \[ 2 \text{AgNO}_{3(s)} \rightarrow 2 \text{Ag}_{(s)} + 2 \text{NO}_{2(g)} + \text{O}_{2(g)} \]

Step 2: Identify Products

From the chemical equation, we identify the products of the decomposition of silver nitrate. The products are silver \( \text{Ag} \), nitrogen dioxide \( \text{NO}_{2} \), and oxygen gas \( \text{O}_{2} \).

Step 3: Match with Given Options

Compare the identified products \( \text{NO}_{2} \) and \( \text{O}_{2} \) with the options provided in the problem. The products match option (b), which lists \( \text{NO}_{2} \) and \( \text{O}_{2} \) as the decomposition products.

Key Concepts

Chemical Equation Balancing

Balancing chemical equations is a crucial skill in chemistry as it ensures the conservation of mass. When a chemical reaction occurs, atoms aren't lost or gained but merely rearranged. Thus, a balanced chemical equation reflects this principle. For instance, when we examine the decomposition of silver nitrate, it initially presents itself as: \[ \mathrm{AgNO}_{3} \rightarrow \mathrm{Ag} + \mathrm{NO}_{2} + \mathrm{O}_{2} \]This equation is unbalanced because the number of atoms of each element does not match on both sides. To balance it, we must adjust coefficients to ensure equal numbers of each type of atom appear on both sides of the equation. For the reaction, the balanced form becomes:\[ 2 \mathrm{AgNO}_{3} \rightarrow 2 \mathrm{Ag} + 2 \mathrm{NO}_{2} + \mathrm{O}_{2} \]Here, every element has an equal count on both the reactant and product sides: - Silver: 2 atoms each side- Nitrogen: 2 atoms each side- Oxygen: 6 atoms each side (2×3 from \(\mathrm{AgNO}_{3}\) and 2×2 from \(\mathrm{NO}_{2}\) plus 2 from \(\mathrm{O}_{2}\))Balancing equations helps in predicting product amounts accurately, which is critical for any experiment or industrial chemical process.

Thermal Decomposition

Thermal decomposition is a type of chemical reaction where a compound breaks down into simpler products when heated. This process is prevalent across various substances, leading to significant changes in composition and properties. Silver nitrate is a prime example, which decomposes upon heating into elemental silver, nitrogen dioxide, and oxygen, as demonstrated by:\[ 2 \mathrm{AgNO}_{3(s)} \rightarrow 2 \mathrm{Ag}_{(s)} + 2 \mathrm{NO}_{2(g)} + \mathrm{O}_{2(g)} \]During thermal decomposition:

• Heat provides the energy needed to break chemical bonds.
• The stability of the compound under heat influences whether decomposition will occur.
• Different compounds decompose at different temperatures.

Understanding thermal decomposition is pivotal in fields like metallurgy, where extracting metals from their ores often involves heating.The products of a decomposition reaction greatly depend on the original compound and its components. In the case of silver nitrate, heating it results in nitrogen dioxide and oxygen gases being expelled, leaving behind metallic silver as a residue.

Silver Nitrate Decomposition

The decomposition of silver nitrate is a classic chemical reaction often studied in chemistry due to its simplicity and clear demonstration of principles. When silver nitrate heats up, the compound transitions from a white crystalline solid into decomposition products:

• Silver metal (\(\mathrm{Ag}\)) is formed as a solid deposit, often as a pale, metallic residue in the reaction container.
• Nitrogen dioxide (\(\mathrm{NO}_{2}\)), a toxic brown gas, is released. This gas, being heavier than air, can pose environmental and health risks if not managed properly.
• Oxygen gas (\(\mathrm{O}_{2}\)) is also produced, contributing to the reaction's gas output and exhibiting the principle of releasing simpler gaseous products.

The balanced chemical equation demonstrates this reaction as:\[ 2 \mathrm{AgNO}_{3} \rightarrow 2 \mathrm{Ag} + 2 \mathrm{NO}_{2} + \mathrm{O}_{2} \]Understanding this decomposition is not only significant for academic purposes but also for practical applications such as in chemical analysis or synthesis of other chemical compounds. The distinct color change and release of gases make it a visually engaging reaction to study in labs.