Problem 196 - A Complete Resource Book in Chemistry for JEE Main

Question

The exothermic formation of \(\mathrm{ClF}_{3}\) is represented by the equation \(\mathrm{Cl}_{2}(\mathrm{~g})+3 \mathrm{~F}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{ClF}_{3}(\mathrm{~g}) ; \Delta \mathrm{H}=-329 \mathrm{~kJ}\) Which of the following will increase the quantity of \(\mathrm{CIF}_{3}\) in an equilibrium mixture of \(\mathrm{Cl}_{2}, \mathrm{~F}_{2}\) and \(\mathrm{ClF}_{3} ?\) (a) increasing the temperature (b) removing \(\mathrm{Cl}_{2}\) (c) increasing the volume of the container (d) adding \(\mathrm{F}_{2}\)

Step-by-Step Solution

Answer

Adding \(\mathrm{F}_{2}\) will increase the quantity of \(\mathrm{ClF}_{3}\).

Step 1: Analyze the Chemical Reaction

The reaction is \[ \mathrm{Cl}_{2}(\mathrm{~g}) + 3 \mathrm{~F}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{ClF}_{3}(\mathrm{~g}) ; \Delta \mathrm{H} = -329 \mathrm{~kJ} \]This reaction is exothermic, meaning it releases heat. According to Le Chatelier’s Principle, the equilibrium will shift to counteract any changes.

Step 2: Evaluate the Impact of Temperature

Increasing the temperature of an exothermic reaction favors the endothermic process (reverse reaction) to absorb the added heat. Thus, it would not increase the amount of \(\mathrm{ClF}_{3}\); instead, it would decrease it.

Step 3: Consider Removing \(\mathrm{Cl}_{2}\)

Removing \(\mathrm{Cl}_{2}\) will shift the equilibrium to the left to replace the removed \(\mathrm{Cl}_{2}\), decreasing the amount of \(\mathrm{ClF}_{3}\) in the system.

Step 4: Assess the Effect of Increasing Volume

Increasing the volume of the container decreases the pressure, which will shift the equilibrium towards the side with more gas molecules according to Le Chatelier’s principle. The reactants side has 4 moles of gas (\(1 \mathrm{~Cl}_{2}\) and \(3 \mathrm{~F}_{2}\)), while the product side has 2 moles (\(2 \mathrm{ClF}_{3}\)). Therefore, increased volume would shift the equilibrium towards the left, decreasing \(\mathrm{ClF}_{3}\).

Step 5: Analyze the Impact of Adding \(\mathrm{F}_{2}\)

Adding \(\mathrm{F}_{2}\) will increase the concentration of one of the reactants, causing the equilibrium to shift to the right to produce more \(\mathrm{ClF}_{3}\). This will increase the quantity of \(\mathrm{ClF}_{3}\) in the equilibrium mixture.

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 changes in its environment. When external conditions such as concentration, temperature, or pressure are altered, the system will adjust itself to counteract those changes and restore equilibrium.
This principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system will shift its position to counteract the effect of the disturbance. This shift in equilibrium can lead to an increase or decrease in the concentration of reactants or products, depending on the type of change applied.
For the reaction \(\mathrm{Cl_{2}(g) + 3F_{2}(g) \rightleftharpoons 2ClF_{3}(g)}\), if we change conditions such as pressure or concentration, Le Chatelier's Principle guides us in predicting whether the reaction will favor the reactants or products. This prediction helps us control the reaction to produce more or less of a desired product.

Exothermic Reaction

An exothermic reaction is characterized by the release of heat to its surroundings. This is evident in the negative sign of \(\Delta H\), which indicates that the reaction releases energy. The heat produced becomes an integral part of the energy balance for the reaction.
In the provided reaction \(\mathrm{Cl_{2} + 3F_{2} \rightleftharpoons 2ClF_{3}}\), \(\Delta H = -329 \, \mathrm{kJ}\), showing that energy is released as \(\mathrm{ClF_{3}}\) forms. In the context of Le Chatelier's Principle, adding heat to the system by increasing temperature would shift the equilibrium towards the endothermic direction (the reverse reaction).
To promote the formation of \(\mathrm{ClF_{3}}\), one should avoid increasing the temperature, as this would lead to less product being formed. Instead, keeping the temperature low favors the exothermic forward reaction, increasing product production.

Equilibrium Shift

The term 'equilibrium shift' refers to the adjustment of the concentrations of reactants and products in a reversible reaction to restore balance when stressed. Stress factors include changes in concentration, pressure, temperature, or volume.
In a scenario where \(\mathrm{F_2}\) is added, the concentration of one of the reactants increases, causing the equilibrium to shift to the right, resulting in the production of more \(\mathrm{ClF_{3}}\). This process illustrates how adjusting concentrations can promote the desired pathway and increase product yield.
Conversely, factors like reducing the concentration of \(\mathrm{Cl_{2}}\) or increasing volume will shift the equilibrium towards the reactant side, decreasing the concentration of \(\mathrm{ClF_{3}}\) produced. Understanding how these shifts occur is crucial for controlling reactions efficiently in industrial processes.

Stoichiometry

Stoichiometry is the study of the quantitative relationships between reactants and products in a chemical reaction. It allows us to predict the amounts of substances consumed and produced.
For the reaction \(\mathrm{Cl_{2} + 3F_{2} \rightleftharpoons 2ClF_{3}}\), the stoichiometric coefficients (1:3:2) are essential for understanding the ratio in which these substances react. This ratio tells us that regardless of the initial amounts, for every mole of \(\mathrm{Cl_{2}}\), three moles of \(\mathrm{F_{2}}\) are needed to produce two moles of \(\mathrm{ClF_{3}}\).
Knowing these relationships helps chemists adjust reactant inputs to control product output precisely. For example, if more \(\mathrm{F_2}\) is desired to produce additional \(\mathrm{ClF_3}\), one must ensure that the proportions align with the stoichiometric coefficients for the reaction to proceed efficiently.