Question

For the given reaction $R\left(g\right)\rightleftharpoons P\left(g\right)$ , In which
case reaction will barely proceeds ?

• A. $K_{eq}>{10}^3$
• B. $K_{eq}<{10}^{-3}$
• C. $K_{eq}=1$
• D. None of the above

Answer 1

The correct option is B $K_{eq}<{10}^{-3}$

$K_{eq}=\frac{[P{]}_{eq}}{[R{]}_{eq}}$
When rate of backward reaction is very high, then during the course of reaction, product will again form reactant.
Therefore product concentartion will decrease and reactant concentration will highly increase i.e. $[P{]}_{eq}<<[R{]}_{eq}$
In reaction $R\left(g\right)\rightleftharpoons P\left(g\right)$ the value of equilibrum constant is $K_{eq}={10}^{-3}$ which is lowest among all other equilibrium constants of reactions given in the options.
Hence, in this case the reaction $R\left(g\right)\rightleftharpoons P\left(g\right)$ will barely proceeds.