Question

# Phosphorus pentachloride decomposes to phosphorus trichloride at high temperatures according to the equation: PCl5(g) ↔ PCl3(g)...

Phosphorus pentachloride decomposes to phosphorus trichloride at high temperatures according to the equation:

PCl5(g) ↔ PCl3(g) + Cl2(g)

At 250° 0.188 M PCl5 is added to the flask. If K c = 1.80, what are the equilibrium concentrations of each gas?

Phosphorus pentachloride decomposes to phosphorus trichloride at high temperatures according to the equation:

PCl5(g) ↔ PCl3(g) + Cl2(g)

At 250° 0.188 M PCl5 is added to the flask. If K c = 1.80, what are the equilibrium concentrations of each gas?

 [PCl5] = 0.0164 M, [PCl3] = 0.172 M, and [Cl2] = 0.172 M [PCl5] = 1.80 M, [PCl3] = 1.80 M, and [Cl2] = 1.80 M [PCl5] = 0.0940 M, [PCl3] = 0.411 M, and [Cl2] = 0.411 M [PCl5] = 4.13 M, [PCl3] = 3.94 M, and [Cl2] = 3.94 M

PCl5 -----------------------------.> PCl3 + Cl2

initial concentration 0.188 M 0 0

change in concentraion -x + x +x

equilibrium concentration 0.188-x + x +x

equilibrium constant , kc = [PCl3] [Cl2]/ [ PCl5]

substitute the equillibriu conentration in the above formula

Kc = X . X/ 0.188-x

1.8 = x2/  0.188-x

x2 + 1.8 x - 0.3384 = 0

on solving the above quadratic we have x = +0.1716 ( negative value of x is rejected)

so the equilibrium concentrations of all gases :

[ PCl5] = 0.188 - 0.1716

= 0.0164M

[ PCl3] = 0.1716 M

[ Cl2] = 0.1716M

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