Simultaneous Equilibria -- part of MCAT?

[cclawfjj]

---

Members do not see this ad.

and if so,

can anyone help me answer this question:

What would happen if 1.5 moles of y were added to a system containing 1.0 mole each of A, B, F and m?
What would be the number of moles of A, B, F and m at equilibrium?

 

[Meatwad]

I haven't been here long, but I'm pretty sure this is the wrong forum for that question.

 

[degoo_]

Its just a bunch of algebra. If you solve the four equations simultaneously you can solve for everything.
You also need to know a volume. Equilibria deal with molars and pressures.. not just moles.

And no, I really don't think that ANY of this is on the MCAT. The math, although easy, is too tedious.

 

[SeventhSon]

are you assuming that A, B, F and m are all at equilibrium at 1.0 mol before Y is added or no?

 

[SeventhSon]

Its just a bunch of algebra. If you solve the four equations simultaneously you can solve for everything.
You also need to know a volume. Equilibria deal with molars and pressures.. not just moles.

And no, I really don't think that ANY of this is on the MCAT. The math, although easy, is too tedious.

um no. Firstly he never said it was gas-phase. Secondly, in the gas phase, you can choose to write equlibrium tables in terms of partial pressure OR moles. The extent of reaction variable is the same either way.

 

[deleted103644]

This is a really simple, if tricky question. Reaction 4 is irreversible, therefore it will go as far to completion as possible.

1 mole A + 1 mole B => 1 mole C + 1 mole D
1 mole C + 1 mole F => 1 mole G + 1 mole H
1 mole H + 1 mole m => 1 mole X
1 mole X + 1 mole y ---> 1 mole z

So at the end, you have

A: 0 moles
B: 0 moles
C: 0 moles
D: 1 mole
F: 0 moles
G: 1 mole
H: 0 moles
m: 0 moles
X: 0 moles
y: 0.5 moles
z: 1 mole
​

Once you realize the last reaction is irreversible and you have a surplus of y, it's trivial to solve.

 

[braluk]

Moving this to MCAT forum where this belongs. Good luck.

 

[SeventhSon]

yeah you're right, but you have to assume that all of the rxns are at equilibrium to do what you did. Since he wrote out "K1, K2, K3" i was under the impression that they were not.