Question

In the reaction, \(\mathrm{N}_{2}+3 \mathrm{H}_{2} \rightarrow 2 \mathrm{NH}_{3}\), ratio by volume of \(\mathrm{N}_{2}, \mathrm{H}_{2}\) and \(\mathrm{NH}_{3}\) is \(1: 3: 2\). This illustrates (1) definite proportions (2) multiple proportions (3) reciprocal proportions (4) gaseous volumes

Short answer

The correct answer is (4) gaseous volumes.

Step-by-step solution

Understand the Given Reaction

The balanced chemical reaction is \(\mathrm{N}_{2}+3 \mathrm{H}_{2} \rightarrow 2 \mathrm{NH}_{3}\). This means 1 volume of nitrogen reacts with 3 volumes of hydrogen to form 2 volumes of ammonia.

Identify the Volume Ratio

From the balanced equation, the ratio by volume of \(\mathrm{N}_{2}, \mathrm{H}_{2}\) and ammonia (\mathrm{NH}_{3}) is 1:3:2.

Analyze the Concept Illustrated

The law illustrated by this volume ratio in a gaseous reaction is the law of combining (gaseous) volumes, which states that when gases react together at constant temperature and pressure, the volumes of the reactants and the products are in simple whole number ratios.

Choose the Correct Option

Based on the analysis, the ratio by volume 1:3:2 illustrates the law of gaseous volumes. Therefore, the correct option is (4) gaseous volumes.

Key concepts

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and the products in a chemical reaction. It's like a recipe where you need the exact amounts of ingredients to get the desired product. In the exercise given, the reaction \(N_{2} + 3H_{2} \rightarrow 2NH_{3}\) tells us that 1 molecule of nitrogen (\(N_{2}\)) reacts with 3 molecules of hydrogen (\(H_{2}\)) to produce 2 molecules of ammonia (\(NH_{3}\)). This relationship is derived from the balanced chemical equation. Key points to remember:

• **Mole Ratios**: For every mole of \(N_{2}\), you need 3 moles of \(H_{2}\) and you will get 2 moles of \(NH_{3}\).
• **Conservation of Mass**: The total mass of reactants is equal to the total mass of products. This aligns with the law of conservation of mass.
• **Ratios**: These mole ratios can also tell us about volume ratios when dealing with gases at constant temperature and pressure.
• **Proportional Relationships**: If you start with a different amount of reactants, the products will change proportionally.
  

Understanding stoichiometry helps in predicting how much product will be formed from given quantities of reactants, which is essential in both laboratory and industrial chemical processes.

Gaseous Reactions

Gaseous reactions involve reactants and products in their gaseous state. In such reactions, it's often useful to focus on volume relationships, especially when the reaction occurs at constant temperature and pressure. For example, the reaction \(N_{2} + 3H_{2} \rightarrow 2NH_{3}\) occurs among gases, nitrogen, hydrogen, and ammonia. The most important points to keep in mind about gaseous reactions include:

• **Ideal Gas Behavior**: Gases in these reactions usually follow the ideal gas law given by \(PV=nRT\), where pressure (\(P\)), volume (\(V\)), number of moles (\(n\)), gas constant (\(R\)), and temperature (\(T\)) are related.
• **Volume Relationships**: As shown in the exercise, 1 volume of \(N_{2}\) reacts with 3 volumes of \(H_{2}\) to produce 2 volumes of \(NH_{3}\). This follows the law of combining volumes.
• **Whole Number Ratios**: The volumes involved in gaseous reactions often combine in simple whole-number ratios.
• **Reversibility and Equilibrium**: Many gaseous reactions are reversible, meaning they can proceed in both forward and reverse directions until they reach equilibrium.
  

Deeper understanding of these reactions helps chemists design processes and predict outcomes of reactions involving gases.

Volume Ratios

Volume ratios are a key concept when dealing with reactions involving gases. These ratios tell us how volumes of gaseous reactants and products relate to each other. In the given exercise, the reaction \(N_{2} + 3H_{2} \rightarrow 2NH_{3}\) exemplifies volume ratios in action. Essential points include:

• **Law of Combining Volumes**: This law, discovered by Joseph Louis Gay-Lussac, states that when gases react together at constant temperature and pressure, their volumes are in simple whole-number ratios.
• **Illustration by Example**: In the exercise, 1 volume of nitrogen reacts with 3 volumes of hydrogen to produce 2 volumes of ammonia, demonstrated by the ratio 1:3:2.
• **Predicting Reaction Volumes**: If you know the volumes of one or more reactants, you can predict the volumes of products using these ratios.
• **Conditions**: These volume relationships hold true only if the reaction is carried out at constant temperature and pressure.
• **Practical Application**: Volume ratios are widely used in industries dealing with gases to optimize production processes and ensure safety measures.
  

Mastering the concept of volume ratios enables you to predict quantities of gaseous substances involved in various chemical reactions, facilitating more efficient experimental and industrial practices.