topscore 1 GC #56

[lkacher]

I'm a little confused on this question:

When 14.250 moles of PCl5 gas is placed in a 3 L container and comes to equilibrium at a constant temperature, 40% of the PCl5 decomposes according to the equation:
PCl5 (g) --> PCl3 (g) + Cl2 (g)
What is the value of Kc for this reaction?

The answer says (1.896)^2 /2.854
I don't really understand the whole explanation they provide and I think they mention an ICE chart without showing it. But I understand that you find the initial concentration by dividing 14.250 mol by 3 L and then multiplying by 40%, which gives 1.896. Can someone please explain where to go from there and how the answer was obtained??

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[lutopie0730]

I'm a little confused on this question:

When 14.250 moles of PCl5 gas is placed in a 3 L container and comes to equilibrium at a constant temperature, 40% of the PCl5 decomposes according to the equation:
PCl5 (g) --> PCl3 (g) + Cl2 (g)
What is the value of Kc for this reaction?

The answer says (1.896)^2 /2.854
I don't really understand the whole explanation they provide and I think they mention an ICE chart without showing it. But I understand that you find the initial concentration by dividing 14.250 mol by 3 L and then multiplying by 40%, which gives 1.896. Can someone please explain where to go from there and how the answer was obtained??

Initial [PCl5] = 14.25 mol / 3L = 4.75 M

Reacted [PCl5] = 4.75M * 40% = 1.896M

PCl5 (g) --> PCl3(g) +Cl2(g)
I 4.75 0 0
C -1.896 +1.896 +1.896
E 2.854 1.896 1.896

Kc=[PCl3][Cl2]/[PCl5]=(1.896)(1.896)/(2.854)

 

[lkacher]

thank you!