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Question: Answered & Verified by Expert
Ammonium sulphide and ammonium selenide on heating dissociates as

(NH4)2S(s) 2NH3(g)+ H2S(g); Kp1 = 9 × 10-3 atm3

(NH4)2Se(s) 2NH3(g) + H2Se(g); Kp2 = 4.5 × 10-3 atm3

The total pressure over the solid mixture at equilibrium is
ChemistryChemical EquilibriumJEE Main
Options:
  • A 0.15 atm
  • B 0.3 atm
  • C 0.45 atm
  • D 0.6 atm
Solution:
1945 Upvotes Verified Answer
The correct answer is: 0.45 atm
NH 4 2 S s 2NH 3 g + H 2 S g 2pp

NH 4 2 Se s 2NH 3 g + H 2 Se g 2qq

K p 1 = p NH 3 2 · p H 2 S = 2 p + 2 q 2 · p = 9.0 × 10 - 3

K p 2 = p NH 3 2 · p H 2 S e = 2 p + 2 q 2 · q = 4.5 × 10 - 3

p q = 2 p = 2 q

K p 1 = 2p + p 2 · p = 9.0 × 10 - 3

p = 0.1 atm and q = 0.1 2 = 0.05

Total pressure = 2p + 2q + p + q = 3p + 3q

                        = 3 × 0.1 + 3 × 0.05 = 0.45 atm

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