Question

In which of the following cases, the reaction goes farthest to completion?

• A. $A\rightleftharpoons B(K={10}^3)$
• B. $P\rightleftharpoons Q(K={10}^{-2})$
• C. $A+B\rightleftharpoons C+D(K=10)$
• D. $X+Y\rightleftharpoons XY(K={10}^{-1})$

Answer 1

The correct option is A $A\rightleftharpoons B(K={10}^3)$

Higher the equilibrium constant, faster the rate of reaction
$A+B\rightleftharpoons C+D$
$\Rightarrow K=\frac{\left[C\right]\left[D\right]}{\left[A\right]\left[B\right]}$
To complete the reaction fastest, the numerator of RHS must be higher.
In reaction $A\rightleftharpoons B$ the value of equilibrum constant is $K={10}^3$ which is higher than other equilibrium constants of reactions given in the options.
hence, the reaction $A\rightleftharpoons B$ will complete fast.