Question

For a reaction, $A+B\rightleftharpoons C+D$, at equilibrium, one-third of $A$ and $B$ are consumed. The value of the equilibrium constant will be:

• A. $0.5$
• B. $0.25$
• C. $0.025$
• D. $5$

Answer 1

The correct option is B $0.25$

Reaction given is,
$\begin{array}{cccccccc}& A& +& B& \rightleftharpoons & C& +& D\\ Initial& C& & C& & 0& & 0\\ Atequilibrium& C(1-\frac{1}{3})& & C(1-\frac{1}{3})& & \frac{C}{3}& & \frac{C}{3}\end{array}$

Also, at equilibrium ($V$ same for all)

$\left[A\right]=\left[B\right]$
and

$\left[C\right]=\left[D\right]$

therefore,
$K=\frac{\left[\frac{C}{3V}\right]\left[\frac{C}{3V}\right]}{\left[\frac{2C}{3V}\right]\left[\frac{2C}{3V}\right]}$

$=\frac{1}{4}=0.25$