I have a midterm next week so i just wanted to make sure i understand:
When we have a solid in a equation like:
A(s)<---> B(g)+ C(g)
and we add more A why do the equilibrium not change and remain the same
K for the reaction you have written is
(B)(C) = Keq. A doesn't enter into the equilibrium AS LONG AS THERE IS A PINCH OF 'A' THERE. It MUST be there in order to establish the equilibrium but whether there is a pinch, or a handful, or a bucket of it, the concentration of A doesn't change. Said another way, in a solution saturated with compound A with solid A on the floor of the beaker or flask, adding more A will not change the concentration of A (you can't make more of it dissolve) and removing some solid A will not change the concentration of A either because removing it will NOT cause some of it to dissolve or ppt. In other words, the amount of A is a constant as long as there is a pinch of it there at equilibrium so we COULD write:
K =(B)(C)/(A) but since A is a constant, then
K = (B)(C)/k and
K*k = (B)(C) and
Keq = (B)(C).
Thank You, It helped with my question
In the equation you provided, A(s) <--> B(g) + C(g), you are describing a reversible reaction where a solid A is in equilibrium with gases B and C.
When more solid A is added to the system, the equilibrium position will not change if A(s) is considered as a pure solid and not as a reactant or product in the equilibrium expression. In other words, the concentration of a pure solid or pure liquid does not appear in the equilibrium expression because it remains constant and does not affect the equilibrium.
The equilibrium is determined by the concentrations of the gases B and C. If you were to add more solid A, it would not have any effect on the concentrations of B and C and therefore will not shift the equilibrium. The only factors that can affect the equilibrium position are changes in temperature, pressure, or concentrations of the reactants or products (in this case, gases B and C).
To determine the effect of changes on an equilibrium, you can use the principles of Le Chatelier's principle. Le Chatelier's principle states that when a system at equilibrium is subjected to a stress (change in temperature, pressure, or concentration), it will shift in a way that helps to relieve that stress. However, since the concentration of a pure solid does not change, adding more solid A does not cause a shift in the equilibrium position.