Quiz 3 Prep #7, setting up ICE box

[Madison Davis 3F]

Problem: For the following reaction, if the initial concentration of PCl3 (g) is 1.0M and x is the equilibrium concentration of P4 (g), what is the expression for the equilibrium constant? PCl3 <--> P4 + Cl2

I balanced the equation... 4PCl3 <--> P4 + 6Cl2

In setting up my ICE box, I realize that the initial for P4 is 0, and that you would add "x" to get your equilibrium value...I still don't understand what to add/subtract for the other components of the reaction? Would I add 6x for Cl2 and subtract 4x from PCl3 because of the stoichiometric coefficients?

Thank you!

[904456845]

4PCl3 <---> P4 + 6Cl2
I: 1.0M 0 0
C: -4x +x +6x
E:1.0-4x +x +6x

the universal rule about ICE Box is that the ratios of "change" are the same as in the formula. Thus, the ratios: PCl3:P4:Cl2=4:1:6, are seen in the formula and the amount of change is the same.

[RaquelAvalos1K]

The expression for the equilibrium constant would thus be:


(x)(6x)⁶ = K_p
(1-4x)⁴


Correct?

[Christian Corrales 3I]

That is what I got.

[VivianDing2G]

Is it K_p or K_c?

[HelenMach 1J]

Kc I believe (talks about equilibrium concentration instead of equilibrium partial pressures)