One mole of pure PCl₅ is placed in an evacuated container and maintained at 250°C. The equilibrium is established at total pressure of 2 atm. What is the partial pressure of chlorine at equilibrium?

Question

One mole of pure PCl₅ is placed in an evacuated container and maintained at 250°C. The equilibrium is established at total pressure of 2 atm. What is the partial pressure of chlorine at equilibrium?
PCl₅(g) ⇌ PCl₃(g) + Cl₂(g); K_p = 1.6 atm

Prashant Kotian · Accepted Answer

Correct answer: C. Let p be the partial pressure of Cl₂. Since initially only PCl₅ was present, P_PCl₃ = P_Cl₂ = p. The total pressure is 2 atm, so P_PCl₅ = 2 - 2p. K_p = (p × p) / (2 - 2p) = 1.6. p² = 3.2 - 3.2p => p² + 3.2p - 3.2 = 0. Solving this gives p = 0.8 atm. Therefore, correct answer is C.

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