Question

Le-Chatelier's principle is not applicable to

• A. \({H}_2(g) + {I}_2(g) \rightleftharpoons 2 {HI}(g)\)
• B. \({Fe}(s) + {S}(s) \rightleftharpoons {FeS}(s)\)
• C. \({N}_2(g) + 3 {H}_2(g) \rightleftharpoons 2 {NH}_3(g)\)
• D. \({N}_2(g) + {O}_2(g) \rightleftharpoons 2 {NO}(g)\)

Hint:

Le-Chatelier's principle is not applicable to pure solids and liquids because their concentrations do not change during chemical equilibrium.

Answer 1

The Correct Option is B

Le-Chatelier's principle applies to systems where changes in temperature, pressure, or concentration cause a shift in equilibrium. However, it does not apply to pure solids and liquids, because their concentrations do not change significantly during a reaction. 
Step 1: {Identifying the Pure Solids and Liquids} 
In reaction (B), Fe and S are pure solids, and thus, their concentrations do not significantly change during the reaction. Therefore, Le-Chatelier's principle is not applicable here. Thus, the correct answer is (B). 
 

Answer 2

Step 1: Understand Le-Chatelier's Principle
Le-Chatelier’s principle states that if a dynamic equilibrium is disturbed by changing the conditions (such as concentration, temperature, or pressure), the system will adjust itself to counteract the change and restore a new equilibrium.
It is generally applicable to systems where the concentration or pressure of gaseous or aqueous species can be altered.

Step 2: Examine the given reaction
\( Fe(s) + S(s) \rightleftharpoons FeS(s) \)
This reaction involves only solid reactants and products.
In equilibrium expressions, the activity of a pure solid is considered to be 1.
As a result, the equilibrium constant for this reaction is not dependent on the concentrations of Fe, S, or FeS.

Step 3: Determine applicability
Since there are no gaseous or aqueous species in the reaction, and changes in pressure or concentration of solids do not affect the system, Le-Chatelier’s principle does not apply here in a meaningful way.

Final Answer: \( Fe(s) + S(s) \rightleftharpoons FeS(s) \)