Question

Equimolar concentrations of $H_2$ and $I_2$ are heated to equilibrium in a 2 litres flask. At equilibrium, the forward and the backward rate constants are found to be equal. What percentage of initial concentration of $H_2$ has reacted at equilibrium ?

• A. 0.33
• B. 0.66
• C. 0.5
• D. 0.4

Answer 1

Answer: (A)

0.33

Answer 2

$\begin{matrix}&H_{2}(g)+&I_{2}(g) {<=>}&2HI(g)&&\\\ \text{Initial }&1\, mol&1\,mol&0&&\\\ \text{At eqm. }&1-x&1-x&2x\,&&\end{matrix}$ $\begin{matrix}Molar conc&\frac{1-x}{2}&\frac{1-x}{2}&\frac{2x}{2}\end{matrix}mol\,L^{-1}$ $K=\frac{\left(2x\right)^{2}}{\left(1-x\right)\left(1-x\right)}=\frac{4x^{2}}{\left(1-x\right)^{2}}$ But $K_{f} k=1\Rightarrow K=1$ $\therefore\frac{2x}{1-x}=1$ or $x=1/ 3$ Percent dissociation $=100/3=33.33\%$