13. At temperature T K, PCI, is 50% dissociated at an equilibrium pressure of 4 atm. At what pressure it would dissociate to the extent of 80% at the same temperature? (1) 0.05 atm (2) 0.60 atm (3) 0.75 atm (4) 2.50 atm
Answers
Answer:
In the question it is given that phosphorus pentachloride is 50% dissociated at 4 atm pressure, at what pressure 60% of the phosphorus pentachloride will dissociate.
- We have to find the pressure of 60% dissociation of the phosphorus pentachloride.
- The chemical equation of dissociation of phosphorus pentachloride is as follows.
initial PCl51⇄PCl30+Cl20At equilibrium PCl51−x⇄PCl3x+Cl2x
- Total number of moles at equilibrium = 1- x + x + x = 1 + x
- We know the relationship between partial pressure of the gas, mole fraction and total pressure.
partial pressure of the gas = mole fraction × total pressuremole fraction = partial pressure of the gastotal pressure of the gasKp=PPCl3×PCl2PPCl5=x1+xP×x1+xP1−x1+xP=x2P1−x2
- Here x = 50% dissociation of the phosphorus pentachloride = 0.5
- Therefore substitute x = 0.5 in the above equation.
Kp=PPCl3×PCl2PPCl5=x1+xP×x1+xP1−x1+xP=x2P1−x2=(0.5)2×41−(0.5)2=1.33
- The x value for 80% dissociation is 0.8.
- Therefore
Kp=PPCl3×PCl2PPCl5=x1+xP×x1+xP1−x1+xP=x2P1−x2(0.8)2×P1−(0.8)2=1.33P=0.75atm.
- Therefore at 0.75 atm of pressure 80% of the dissociation of the phosphorus pentachloride occurs.
Explanation:
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