Question

At a certain temperature, only $50\%$ $HI$ is dissociated into $H_2$ and $I_2$ at equilibrium. The equilibrium constant is :

• A. 1
• B. 3
• C. 0.5
• D. 0.25

Answer 1

Answer: (D)

0.25

Answer 2

$\underset{1 - \alpha}{2HI} {<=>} \underset{\frac{\alpha}{2}}{H_3} +\underset{\frac{\alpha}{2}}{I_2}$
$K_{eq} =\frac{\left(\frac{\alpha}{2}\right)^{2}}{\left(1-\alpha\right)^{2}}=\frac{\alpha^{2}}{4\left(1-\alpha\right)^{2}}$
$K_{eq} =\frac{\left(\frac{1}{2}\right)^{2}}{4\left(1/2 \right)^{2}}=\frac{1}{4}$