Problem 36 - A Complete Resource Book in Chemistry for JEE Main

Question

For the chemical reaction \(3 \mathrm{X}(\mathrm{g})+\mathrm{Y}(\mathrm{g}) \rightleftharpoons \mathrm{X}_{3} \mathrm{Y}(\mathrm{g})\), the amount of \(\mathrm{X}_{3} \mathrm{Y}\) at equilibrium is affected by (a) temperature and pressure (b) temperature only (c) pressure only (d) temperature, pressure and catalyst

Step-by-Step Solution

Answer

(a) Temperature and pressure

Step 1: Assess the Reaction Type

The reaction given is an equilibrium reaction, meaning it can proceed in both forward and reverse directions. Such reactions are typically affected by changes in temperature, pressure, and catalysts.

Step 2: Consider Temperature Effects

For equilibrium reactions, changing the temperature can alter the position of equilibrium based on the enthalpy change of the reaction. If the reaction is exothermic, increasing temperature shifts equilibrium to the left (favoring reactants), and vice versa for endothermic reactions.

Step 3: Consider Pressure Effects

In reactions involving gases, pressure changes shift equilibrium toward the side with fewer moles of gas, according to Le Chatelier's principle. In this case, the reaction goes from 4 moles (3 moles of X and 1 mole of Y) to 1 mole of X₃Y, so increasing pressure will favor the formation of X₃Y.

Step 4: Consider Catalyst Effects

Catalysts speed up the rate at which equilibrium is reached, but they do not change the position of equilibrium or the amount of products and reactants at equilibrium. Thus, catalysts do not affect the amount of X₃Y at equilibrium.

Key Concepts

Le Chatelier's Principle

Le Chatelier's principle is a fundamental concept in chemistry that helps us understand how a system at equilibrium responds to external changes. When a system at equilibrium experiences a change in concentration, temperature, or pressure, it adjusts itself to counteract the change and restore a new equilibrium.
For chemical reactions like the one given, where 3 moles of X react with one mole of Y to form X₃Y, Le Chatelier's principle allows us to predict how the equilibrium will shift.

• If there's an increase in the concentration of reactants (X or Y), the system will shift to the right, producing more X₃Y.
• A decrease in reactants will cause the equilibrium to shift to the left, reducing X₃Y production.

Using this principle, we can predict the effects of changes in the reaction conditions on the equilibrium, always aiming to minimize the impact of any change and establish a new balance.

Temperature Effects on Equilibrium

Temperature changes can significantly affect equilibrium reactions, predominantly through the principle of endothermic and exothermic reactions. An exothermic reaction is one that releases heat, while an endothermic reaction absorbs heat.
In the given reaction, knowing whether it's endothermic or exothermic would allow us to predict the direction of the equilibrium shift:

• If the reaction is exothermic, increasing the temperature will favor the reverse reaction, shifting the equilibrium to the left, towards the reactants.
• Conversely, if it is endothermic, increasing temperature will favor the forward reaction, producing more X₃Y.

Overall, temperature is a critical factor as it determines not only the rate of the reaction but also the favorability of the formation of products or reactants.

Pressure Effects on Equilibrium

Pressure changes primarily affect equilibrium reactions that involve gases, as it exploits the relationship between pressure and volume. Le Chatelier's principle informs us that when a system at equilibrium is subjected to an increase in pressure, the equilibrium will shift toward the side with fewer moles of gas.
In the given reaction, the reactants consist of 3 moles of X and one mole of Y—a total of 4 moles—while the product X₃Y consists of only 1 mole.

• An increase in pressure will therefore shift the equilibrium towards the product side, favoring the formation of X₃Y because it has fewer moles of gas.
• Conversely, a decrease in pressure would shift the equilibrium towards the reactants, as they occupy a larger volume.

Understanding the pressure effects allows chemists to manipulate conditions to favor the formation of products or reactants, further guiding the practical applications of the reaction.