7.19. A sample of pure PCl5 was introduced into an evacuated vessel at 473 K. After equilibrium was reached, the concentration of PCl5 was found to be 0.5 x 10-1 mol L-1. If Kc is 8.3 x 10-3 what are the concentrations of PCl3 and Cl2 at equilibrium?
7.19. A sample of pure PCl5 was introduced into an evacuated vessel at 473 K. After equilibrium was reached, the concentration of PCl5 was found to be 0.5 x 10-1 mol L-1. If Kc is 8.3 x 10-3 what are the concentrations of PCl3 and Cl2 at equilibrium?
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1 Answer
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Let the initial molar concentration of PCl5 per litre = x mol
Molar concentration of PCl5 at equilibrium = 0.05 mol
Therefore, moles of PCl5 decomposed = (x – 0.05) mol
Moles of PCl3 formed = (x – 0.05) mol
Moles of Cl2 formed = (x – 0.05) mol
The molar conc./litre of reactants and products before the reaction and at the equilibrium point are:PCl5
PCl3
Cl2
Initial moles/litre
x
0
0
At equilibrium
0.05
x – 0.05
x – 0.05
Kc = [PCl3] [Cl2] / [PCl5]
=> 8.3 x 10-3 = (x – 0.05)2 / 0.05
=> (x – 0.05) = (4.15 x 10-4)1/2 = 2.037 x 10-2 = 0.02 moles
=> x = 0.05 + 0.02 = 0.07 mol
Therefore, at equilibrium:
Moles of PCl3 formed = (x – 0.05) mol = 0.07 – 0.05 = 0.02 mol
Moles of C...more
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