Simple equilibrium question

[Monkeymaniac]

---

Members don't see this ad.

I'm having trouble understanding the following TBR question

X+Y->Z+W (all coefficients are 1)

All of the following affect the reactant/product ratios of the equilibrium mixture except

A. increasing the volume of the reaction vessel
B. heating the reactino vessel
C. colling the reaction vessel
D. adding reactant to the reaction vessel

The answer is A, since all the coefficients are 1.
But why can't D also be the answer? reactant/product ratio is eq. constant, is it not? Then adding a reaction will simply displace the equilibrium followed by the establishment of the equilibrium, at which point the product/reactant ratio should be the same again. Am I missing something here? Thanks in advance.

 

[venacontracta]

By "reactant/product ratio" the question means reaction quotient, Q, not equilibrium constant. Adding a reactant will change Q for some period of time (until the equilibrium is reestablished)

 

[rls303]

By "reactant/product ratio" the question means reaction quotient, Q, not equilibrium constant. Adding a reactant will change Q for some period of time (until the equilibrium is reestablished)

Hi,
a quick question, I always thought Q, was product/reactants and the same thing as Keq except initially? Or am I totally off?

 

[PiBond]

Hi,
a quick question, I always thought Q, was product/reactants and the same thing as Keq except initially? Or am I totally off?

Q is denoted by products/reactants but it's for a given setup that is not necessarily at equilibrium. We use Q to compare to Keq to figure out what direction the reaction will shift. when Q = Keq then we're at equilibrium