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JEE Main 20265 AprilEvening Shift
Exam
JEE Main
Year
2026
Date
5 April
Shift
Evening Shift
Subject
Chemistry
Chapter
Chemical Equilibrium

JEE Main 2026 · 5 April · Evening Shift · Chemistry · Chemical Equilibrium

The reaction A(g) leftharpoons B(g) + C(g) was initiated with the...

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

Options

  1. Ax2a2+x2×p\dfrac{x^2}{a^2 + x^2} \times p
  2. Bx2a2−x2×p\dfrac{x^2}{a^2 - x^2} \times p
  3. Ca+x2x2×p\dfrac{a + x^2}{x^2} \times p
  4. Da2−x2x2×p\dfrac{a^2 - x^2}{x^2} \times p

Correct answer

B. x2a2−x2×p\dfrac{x^2}{a^2 - x^2} \times p

Step-by-step solution

The reaction is A(g)⇌B(g)+C(g)A(g) \rightleftharpoons B(g) + C(g)

Initial moles: aa for AA, 00 for BB, 00 for CC

Moles at equilibrium: (a−x)(a - x) for AA, xx for BB, xx for CC

Total moles at equilibrium =(a−x)+x+x=a+x= (a - x) + x + x = a + x

Partial pressures at equilibrium:

pA=a−xa+xpp_A = \dfrac{a - x}{a + x} p

pB=xa+xpp_B = \dfrac{x}{a + x} p

pC=xa+xpp_C = \dfrac{x}{a + x} p

The equilibrium constant KpK_p is given by:

Kp=pB⋅pCpAK_p = \dfrac{p_B \cdot p_C}{p_A}

Kp=(xa+xp)(xa+xp)a−xa+xpK_p = \dfrac{\left(\dfrac{x}{a + x} p\right) \left(\dfrac{x}{a + x} p\right)}{\dfrac{a - x}{a + x} p}

Kp=x2(a+x)(a−x)pK_p = \dfrac{x^2}{(a + x)(a - x)} p

Kp=x2a2−x2pK_p = \dfrac{x^2}{a^2 - x^2} p

Answer: x2a2−x2×p\dfrac{x^2}{a^2 - x^2} \times p
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