For the equilibrium PCl5(g) PCl3(g) + Cl2(g), Kc = 2.0 × 101 at 240°C. If pure PCl5 is placed in a 1.00-L container and allowed to come to equilibrium, and the equilibrium concentration of PCl3(g) is 0.27 M, what is the equilibrium concentration of PCl5(g)?

Respuesta :

Answer:

the equilibrium concentration of [PCl₅] is 3.64*10⁻³ M

Explanation:

for the reaction

PCl₅(g) → PCl₃(g) + Cl₂(g)

where

Kc= [PCl₃]*[Cl₂]/[PCl₅] = 2.0*10¹ M = 20 M

and [A] denote concentrations of A

if initially the mixture is pure PCl₅ , then it will dissociate according to the reaction and since always one mole of PCl₃(g) is generated with one mole of Cl₂(g) , the total number of moles of both at the end is the same → they have the same concentration → [PCl₃(g)] = [Cl₂]=0.27 M

therefore

Kc= [PCl₃]*[Cl₂]/[PCl₅] = 0.27 M* 0.27 M /[PCl₅] = 20 M

[PCl₅]  =  0.27 M* 0.27 M / 20 M = 3.64*10⁻³ M

[PCl₅]  = 3.64*10⁻³ M

the equilibrium concentration of [PCl₅] is 3.64*10⁻³ M

The equilibrium concentration of PCl5 is 0.0036 M.

The equation of the reaction is; PCl5(g) ⇄ PCl3(g) + Cl2(g)

The number of moles of PCl3 at equilibrium is = 0.27 M ×  1.00-L = 0.27 moles

Now;

Kc = [PCl3] [Cl2]/[PCl5]

Kc =  2.0 × 10^1 or 20

We can see that;

Number of moles  of PCl3 = Number of moles of Cl2 = 0.27 moles

Let the equilibrium concentration of PCl5 be x

20 = (0.27)^2/x

x =  (0.27)^2/20

x = 0.0036 moles

Since the volume does not change;

equilibrium concentration of PCl5 = 0.0036 moles/1.00-L = 0.0036 M

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