Problem 41 - A Complete Resource Book in Chemistry for JEE Main

Question

In what manner will increase of pressure affect the following equation? \(\mathrm{C}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \rightleftharpoons \mathrm{CO}(\mathrm{g})+\mathrm{H}_{2}(\mathrm{~g})\) (a) shift in the reverse direction (b) shift in the forward direction (c) increase in the yield of hydrogen (d) no effect

Step-by-Step Solution

Answer

(a) shift in the reverse direction.

Step 1: Understanding the Reaction

The given reaction is \( \mathrm{C} (\mathrm{s}) + \mathrm{H}_2 \mathrm{O} (\mathrm{g}) \rightleftharpoons \mathrm{CO} (\mathrm{g}) + \mathrm{H}_2 (\mathrm{g}) \), which is an equilibrium reaction involving solids and gases.

Step 2: Identify Gaseous Reactants and Products

In this reaction, the gaseous components are \( \mathrm{H}_2 \mathrm{O} (\mathrm{g}) \) on the reactant side and \( \mathrm{CO} (\mathrm{g}) + \mathrm{H}_2 (\mathrm{g}) \) on the product side. We count the total moles of gas on each side.

Step 3: Count Moles of Gas on Each Side

On the reactant side, there is 1 mole of \( \mathrm{H}_2 \mathrm{O} (\mathrm{g}) \). On the product side, there are 1 mole of \( \mathrm{CO} (\mathrm{g}) \) and 1 mole of \( \mathrm{H}_2 (\mathrm{g}) \) - totaling 2 moles of gas.

Step 4: Apply Le Chatelier's Principle

According to Le Chatelier's Principle, an increase in pressure will favor the side with fewer moles of gas. In this reaction, the reactant side has 1 mole of gas, while the product side has 2 moles of gas.

Step 5: Predict the Effect of Increased Pressure

As pressure increases, the equilibrium will shift toward the side with fewer moles of gas to counteract the change, which is the reactant side in this case (reverse direction).

Key Concepts

Equilibrium Shift

In chemical reactions that are in a state of equilibrium, changes in external conditions can cause the position of equilibrium to shift. This concept is rooted in Le Chatelier's Principle, which helps predict how a system at equilibrium will respond to changes in concentration, temperature, or pressure.

When a change occurs, such as an increase in pressure, the equilibrium shifts in a direction that would counteract this change. Imagine a balance — adding weight to one side causes a shift as the system tries to rebalance itself. In our given reaction, if pressure increases, the reaction will adjust to reduce this pressure.

By understanding how equilibrium shifts according to external changes, we can predict which direction a reaction will prefer under different conditions. This knowledge is crucial, especially in industrial applications, where controlling product yield is often desired.

Effect of Pressure on Equilibrium

The effect of pressure on equilibrium plays a major role in how a reaction proceeds. When we talk about pressure changes, we're usually discussing reactions involving gases. This is because gases are compressible, and their volumes can significantly change with pressure differences.

In our specific reaction, increasing the pressure pushes the equilibrium toward the side with fewer moles of gas. This response is a direct application of Le Chatelier's Principle. The system seeks to minimize the impact of pressure by favoring the side of the reaction with less gas volume to decrease the overall system pressure.

• An increase in pressure leads to a shift toward the side with fewer gas moles.
• A decrease in pressure shifts it away from that side.

Understanding this is crucial not just for academics, but for practical chemistry processes such as gas synthesis or industrial gas reactions.

Moles of Gas in Reaction

In any given chemical reaction, counting the moles of gas on each side can provide valuable insight into how equilibrium might shift under pressure changes. This is because gases contribute to the pressure exerted by a reaction.

Taking our reaction example — \( ext{C (s) + H}_2 ext{O (g)} ightleftharpoons ext{CO (g) + H}_2 ext{(g)} \) —We note that the reactant side has 1 mole of gas, coming from \( ext{H}_2 ext{O (g)}\). Meanwhile, the product side has 2 moles of gas, originating from \( ext{CO (g)}\) and \( ext{H}_2 ext{(g)}\).

This disparity in the number of gas moles helps in predicting how pressure changes will affect equilibrium. Recognizing the balance of moles between reactants and products can guide decisions in chemical manufacturing where handling pressure efficiently can influence product yields and processes efficiency.