Question

At certain temperature $50$% of $HI$ is dissociated into $H_2$ and $I_2$, the equilibrium constant is :

• A. $1.0$
• B. $3.0$
• C. $0.5$
• D. $0.25$

Answer 1

The correct option is D $0.25$

$\alpha =$50%$=\frac{50}{100}=0.5$
$\underset{\underset{(2-2\alpha )}{2}}{2HI}\rightleftharpoons \underset{\underset{\alpha }{0}}{H_2}+\underset{\underset{\alpha }{0}}{I_1}$
$K=\frac{{\alpha }^2}{(2-2\alpha {)}^2}=\frac{0.5\times 0.5}{(2-2\times 0.5{)}^2}=0.25$