For the reaction `A+BhArr C+D`, the equilibrium constant is K. what would be the value of the reaction quotient (Q), when the reaction just starts annd when it reaches equilibrium?

Explanation

For the given reaction, equilibrium constant,
`K=([C]_(eq)xx[D]_(eq))/([A]_(eq)xx[B]_(eq))`, where `[A]_(eq),[B]_(eq),[C]_(eq) and [D]_(eq)` are the equilibrium concentrations of A, B, C and D respectively.
For the given reaction, the reaction quotient (Q) at any moment during the course of the reaction,
`Q=([C]xx[D])/([A]xx[B])`, wehre [A], [B], [C] and [D] are the molar concentrations of A, B,C and D respectively at the moment under consideration.
(i) Initially: `[C]=0,[D]=0`. therefore, Q=0
(ii) At the equilibrium state [A]=`[A]_(eq),[B]=[B]_(eq),[C]=[C]_(eq) and [D]=[D]_(eq)`. hence, Q=K.