Problem 133 - A Complete Resource Book in Chemistry for JEE Main

Question

In the reaction \(4 \mathrm{NH}_{3}(\mathrm{~g})+5 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 4 \mathrm{NO}(\mathrm{g})+6 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\) when \(1 \mathrm{~mol}\) of ammonia and \(1 \mathrm{~mol}\) of \(\mathrm{O}_{2}\) are made to react to completion then (a) \(1.0 \mathrm{~mol}\) of \(\mathrm{H}_{2} \mathrm{O}\) is produced (b) \(1.0 \mathrm{~mol}\) of \(\mathrm{NO}\) will be produced (c) all the ammonia will be consumed (d) all the oxygen will be consumed

Step-by-Step Solution

Answer

Only statement (d) is correct: all oxygen is consumed.

Step 1: Determine the Limiting Reactant

To find the limiting reactant, we start by comparing the mole ratio of NH₃ to O₂ from the balanced equation, which is \(4:5\). Given that we have \(1\) mole of NH₃ and \(1\) mole of O₂, calculate the ratio: \( \frac{1}{4} \) for NH₃ and \( \frac{1}{5} \) for O₂. Since \( \frac{1}{5} < \frac{1}{4} \), O₂ is the limiting reactant.

Step 2: Calculate Products Formed

Using O₂ as the limiting reactant, determine the amount of NO and H₂O produced. From the balanced equation, \(5\) moles of O₂ produce \(4\) moles of NO, and \(5\) moles of O₂ produce \(6\) moles of H₂O. Therefore, \(1\) mole of O₂ (as it is limiting) will produce \( \frac{4}{5} \times 1 = 0.8 \) moles of NO and \( \frac{6}{5} \times 1 = 1.2 \) moles of H₂O.

Step 3: Determine Amount of Reactants Consumed

Since O₂ is the limiting reactant and will be completely consumed, the remaining amount of NH₃ used can be calculated. From the ratio, \(5\) moles of O₂ react with \(4\) moles of NH₃. Thus, \(1\) mole of O₂ will react with \( \frac{4}{5} \) moles of NH₃, leaving \(1 - \frac{4}{5} = 0.2\) moles of NH₃ unreacted.

Step 4: Conclusion Based on Reaction Results

Summarizing the findings: (a) \(1.0\) mole of H₂O is not produced, as it is \(1.2\) moles. (b) \(1.0\) mole of NO is not produced, as it is \(0.8\) moles. (c) All the ammonia will not be consumed as \(0.2\) moles remain. (d) All the oxygen will be consumed, as it is the limiting reactant.

Key Concepts

Stoichiometry

Stoichiometry is a branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It involves calculations based on the principles of conservation of mass and the laws of definite and multiple proportions.
Understanding stoichiometry helps us determine the amount of reactants needed and the amount of products formed in a chemical reaction. This is crucial for predicting yields and scaling reactions for practical applications.
The process often involves:

• Using the coefficients from the balanced chemical equation to determine mole ratios.
• Calculating molar masses for converting between moles and grams.
• Identifying the limiting reactant to find maximum possible yield.

Whether you are a student or a professional chemist, mastering stoichiometry is essential for understanding and applying chemical reactions effectively.

Balanced Chemical Equation

A balanced chemical equation is a representation of a chemical reaction with the same number of atoms of each element on both sides of the equation. This balance honors the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.
Balancing chemical equations is a critical skill in chemistry. It ensures that the equations properly reflect real-life reactions. To balance an equation, adjust the coefficients (the numbers in front of molecules in the equation) until each type of atom is equal on both sides.
For example, with the equation \[4 \mathrm{NH}_{3}(\mathrm{~g}) + 5 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 4 \mathrm{NO}(\mathrm{g}) + 6 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \] We can see that both the reactants and products have:

• 4 nitrogen atoms
• 10 hydrogen atoms
• 10 oxygen atoms

This balance allows chemists to correctly predict the amounts of products generated and reactants consumed in chemical processes.

Chemical Reactions

Chemical reactions are processes where reactants transform into products through chemical changes. These transformations involve breaking chemical bonds in reactants and forming new ones in products.
Reactions can be categorized into types like synthesis, decomposition, single replacement, and double replacement, each with unique patterns and outcomes.
In chemical reactions:

• The reactants are the starting substances on the left side of the equation.
• The products are on the right side and result from the reactants' interactions.
• Energy is often either absorbed or released, sometimes visible through light, heat, or color change.

Understanding these transformations and their energy changes is key to developing new materials, fuels, and pharmaceuticals.

Mole Ratio

Mole ratio is a stoichiometric term used to describe the proportion of moles of one substance to the moles of another substance in a chemical reaction. These ratios come directly from the coefficients of a balanced chemical equation.
For the reaction \[4 \mathrm{NH}_{3}(\mathrm{~g}) + 5 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 4 \mathrm{NO}(\mathrm{g}) + 6 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \] The mole ratio from NH₃ to O₂ is 4:5, meaning 4 moles of ammonia react with 5 moles of oxygen. Similarly, the ratio for O₂ to NO is 5:4. These ratios are crucial for:

• Determining the limiting reactant, the substance that runs out first and limits the amount of product formed.
• Calculating mass of products generated from a given mass of reactants.
• Optimizing reactant quantities for industrial processes to minimize waste.

Understanding and using these ratios is a foundational skill for analyzing chemical reactions quantitatively.