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For the reaction, $PC{l_5}\left( g \right) \rightleftharpoons PC{l_3}\left( g \right) +
C{l_2}\left( g \right)$ The forward reaction at constant temperature is favoured by:
A. Introducing an inert gas at constant volume
B. Introducing chlorine gas at constant volume
C. Introducing an inert gas at constant pressure
D. None of the above

Last updated date: 18th Jun 2024
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Hint: We can make the reaction to move in a forward direction at constant temperature by various ways such as by increasing the mass of reactants or by increasing the volume of the container or by adding a rare gas to the system.

Complete Step by step answer: In the reaction $PC{l_5}\left( g \right) \rightleftharpoons PC{l_3}\left( g \right) + C{l_2}\left( g \right)$ ,$PC{l_5}$ represents Phosphorus pentachloride, $PC{l_3}$ represents phosphorus trichloride and $C{l_2}$ represents chlorine gas. Both the reactant and products are in a gaseous state. Phosphorus pentachloride gets decomposed to form potassium trichloride and chlorine gas. It is an endothermic reaction i.e., energy is required for the decomposition of the reactant. The arrow mark shown in the reaction represents that it is a reversible reaction i.e., reactants decompose to form products and the given products can be used to form phosphorus pentachloride (composition reaction).
The forward reaction i.e., the reaction in which phosphorus pentachloride decomposes to phosphorus trichloride and chlorine gas at constant temperature is favoured by using an inert gas at constant pressure which increases volume and reduces the concentration of reactants. When an inert gas is introduced in the container at fixed volume, the total pressure gets increased but its equilibrium is not changed. Similarly, when we introduce more chlorine gas at constant volume, the reaction would not continue to be in a forward direction.
The forward reaction can also be brought by increasing the volume of the container, by introducing more $PC{l_5}$ at constant volume, etc.

Therefore, option C is correct.

Note: We should remember that when we add inert gas to the reaction at constant pressure, it will lead to the increase in total volume and thus decrease in concentration of reactants.Keep in mind the reaction will not proceed untill it does not have required activation nenrgy.