Question

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

Answer 1

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 , k_{c =} [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