JEE Mains · Chemistry · STD 11 - 6.1. Equilibrium - 1 (chemical Equilibrium)

The reaction \(A(g) \rightleftharpoons B(g) + C(g)\) was initiated with the amount '\(a\)' of \(A(g)\). At equilibrium it is found that the amount of \(A(g)\) remaining is \((a - x)\) at a total pressure of \(p\).
The equilibrium constant \(K_p\) of the reaction can be calculated from the expression :

A \(\dfrac{x^2}{a^2 + x^2} \times p\)
B \(\dfrac{x^2}{a^2 - x^2} \times p\)
C \(\dfrac{a + x^2}{x^2} \times p\)
D \(\dfrac{a^2 - x^2}{x^2} \times p\)

Verified Solution

Answer & Solution

Correct Answer

(B) \(\dfrac{x^2}{a^2 - x^2} \times p\)

Step-by-step Solution

Detailed explanation

The reaction is \(A(g) \rightleftharpoons B(g) + C(g)\) Initial moles: \(a\) for \(A\), \(0\) for \(B\), \(0\) for \(C\) Moles at equilibrium: \((a - x)\) for \(A\), \(x\) for \(B\), \(x\) for \(C\) Total moles at equilibrium \(= (a - x) + x + x = a + x\) Partial pressures at…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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