Question

Determine the value of equilibrium constant $\left(K_c\right)$ for the reaction $A_{2\left(g\right)}+B_{2\left(g\right)}\leftrightharpoons 2A{B}_{\left(g\right)}$
If $10$ moles of $A_2,$ $15$ moles of $B_2$ and $5$ moles of $AB$ are placed in a $2\text{L}$ vessel and allowed to come to equilibrium. The final concentration of $AB$ is $7.5\text{M}$.

• A. $4.5$
• B. $1.5$
• C. $3.0$
• D. $6.0$

Answer 1

The correct option is A $4.5$

$\begin{array}{cccccc}& A_{2\left(g\right)}& +& B_{2\left(g\right)}& \leftrightharpoons & 2A{B}_{\left(g\right)}\\ \text{Initial conc.}& 5& & 7.5& & 2.5\\ \text{at eqm}& 5-x& & 7.5-x& & 2.5+2x\end{array}$
According to the question the final concentration of $AB$ is $7.5\text{M}$.
$\therefore 2.5+2x=7.5\Rightarrow x=2.5$
The equilibrium constant is $K_c=\frac{(7.5{)}^2}{2.5\times 5}=4.5$