Problem 2 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The equation that represents the water-gas shift reaction is: (a) \(\mathrm{CH}_{4}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \frac{1270 \mathrm{~K}}{\mathrm{Ni}} \rightarrow \mathrm{CO}(\mathrm{g})+3 \mathrm{H}_{2}(\mathrm{~g})\) (b) \(2 \mathrm{C}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g})+4 \mathrm{~N}_{2}(\mathrm{~g}) \stackrel{1273 \mathrm{~K}}{\longrightarrow}\) \(2 \mathrm{CO}(\mathrm{g})+4 \mathrm{~N}_{2}(\mathrm{~g})\) (c) \(\mathrm{C}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \stackrel{1270 \mathrm{~K}}{\longrightarrow} \mathrm{CO}(\mathrm{g})+\mathrm{H}_{2}(\mathrm{~g})\) (d) \(\mathrm{CO}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \frac{673 \mathrm{~K}}{\text { Catalyst }} \mathrm{CO}_{2}(\mathrm{~g})+\mathrm{H}_{2}(\mathrm{~g})\)

Step-by-Step Solution

Answer

The answer is reaction (d).

Step 1: Define the Water-Gas Shift Reaction

The water-gas shift reaction is a chemical reaction that involves carbon monoxide (CO) and water vapor (H2O) reacting to form carbon dioxide (CO2) and hydrogen gas (H2). The general chemical equation for this reaction is: \( \text{CO(g)} + \text{H}_2\text{O(g)} \rightarrow \text{CO}_2\text{(g)} + \text{H}_2\text{(g)} \).

Step 2: Analyze Each Given Reaction

Let's review the given reactions:(a) \( \text{CH}_4\text{(g)}+\text{H}_2\text{O(g)} \rightarrow \text{CO}\text{(g)}+3 \text{H}_2\text{(g)} \)This reaction involves methane and is not the water-gas shift reaction.(b) \( 2 \text{C}\text{(s)}+\text{O}_2\text{(g)}+4 \text{~N}_2\text{(g)} \rightarrow 2 \text{CO(g)} +4 \text{~N}_2\text{(g)} \)This reaction forms carbon monoxide from oxygen and does not involve water vapor directly, so it is not the water-gas shift reaction.(c) \( \text{C}\text{(s)}+\text{H}_2\text{O(g)} \rightarrow \text{CO}\text{(g)}+\text{H}_2\text{(g)} \)This reaction involves carbon and water vapor to form CO and H2, resembling a form of shift reaction but without forming CO2.(d) \( \text{CO}\text{(g)}+\text{H}_2\text{O(g)} \rightarrow \text{CO}_2\text{(g)}+\text{H}_2\text{(g)} \)In this reaction, carbon monoxide and water vapor react to form carbon dioxide and hydrogen, matching the water-gas shift reaction.

Step 3: Identify the Correct Reaction

Based on Step 2, the reaction that exactly follows the pattern of the water-gas shift reaction is:\( \text{CO}\text{(g)}+\text{H}_2\text{O(g)} \rightarrow \text{CO}_2\text{(g)}+\text{H}_2\text{(g)} \).This aligns perfectly with the definition of a water-gas shift reaction, with all components in place: CO, H2O, CO2, and H2.

Key Concepts

Chemical Reaction Analysis

Chemical reaction analysis is essential to understand and categorize reactions like the water-gas shift reaction. When analyzing a chemical reaction, we identify the reactants, products, and whether the reaction meets specific criteria for a known reaction type.
This involves looking at the balanced chemical equation, noting each chemical species, the state of matter (solid, liquid, gas), and the stoichiometry, which tells us the proportions in which the reactants and products participate.
For example, the water-gas shift reaction is characterized by carbon monoxide (\( \text{CO(g)} \)) and water vapor (\( \text{H}_2\text{O(g)} \)) reacting to form carbon dioxide (\( \text{CO}_2\text{(g)} \)) and hydrogen gas (\( \text{H}_2\text{(g)} \)).

• Identify the reactants: In the water-gas shift reaction, these are CO and H2O.
• Identify the products: These are CO2 and H2.
• Ensure the reaction is balanced: Confirm that the number of atoms for each element is equal on both sides of the equation.

Analyzing these elements helps pinpoint which reactions fit the mold of a specific type, such as the water-gas shift reaction among a given set of equations.

Stoichiometry

Stoichiometry is the quantitative study of reactants and products in a chemical reaction. It is the method used to calculate the precise amounts of reactants required and the products formed.
In the context of the water-gas shift reaction (\( \text{CO(g)} + \text{H}_2\text{O(g)} \rightarrow \text{CO}_2\text{(g)} + \text{H}_2\text{(g)} \)), stoichiometry helps us understand that one molecule of carbon monoxide reacts with one molecule of water to produce one molecule of carbon dioxide and one molecule of hydrogen gas.

• Molar Ratios: The equation provides a 1:1:1:1 molar ratio of CO, H2O, CO2, and H2.
• Balancing Equations: Ensures that the same number of each type of atom appears on both sides of the equation, adhering to the law of conservation of mass.
• Practical Uses: Stoichiometry calculations can be used to predict how much product will form from a given amount of reactant, or how much reactant is needed to form a desired amount of product.

Mastering stoichiometry allows chemists to plan reactions efficiently, minimize waste, and meet specific chemical production needs effectively.

Reaction Mechanism

A reaction mechanism describes the step-by-step sequence of events at the molecular level that leads to the transformation of reactants to products in a chemical reaction.
For the water-gas shift reaction, the mechanism can involve multiple stages, often dependent on conditions like temperature and the presence of catalysts.

• Initial Step: Carbon monoxide (\( \text{CO} \)) may first adsorb onto the surface of a catalyst.
• Intermediate Formation: Water vapor (\( \text{H}_2\text{O} \)) interacts with the adsorbed CO, potentially forming an intermediate species.
• Final Step: The intermediate decomposes to release carbon dioxide (\( \text{CO}_2 \)) and hydrogen gas (\( \text{H}_2 \)).

Understanding the mechanism is crucial for controlling reaction conditions to optimize output and efficiency.
In industrial settings, insights into mechanisms aid in designing better catalysts that enhance the rate of production and selectivity of the desired products.