Question

For the following reaction $K_c=4$ at a certain temperature $2NOCl\left(g\right)\rightleftharpoons 2NO\left(g\right)+2NO\left(g\right)+{Cl}_2\left(g\right).$ What concentration of NOCl must be put into reaction vessel at the start? In order that the equilibrium concentration of NOCl will be 1 M.

• A. 3.75 M
• B. 3.25 M
• C. 3.50 M
• D. 3 M

Answer 1

The correct option is D 3 M

$\alpha \to \text{degree of dissociation.}$

$\begin{array}{c}\text{According to question:}\\ x-2\alpha x=1-\left(i\right)\\ \text{And,}\\ k_c=\frac{[NO{]}^2\left[C{l}_2\right]}{[NOCl{]}^2}\end{array}$

$\begin{array}{cc}\Rightarrow 4& =\frac{(2\alpha x{)}^2\alpha x}{(x-2\alpha x{)}^2}\\ \Rightarrow 4& =\frac{4{\alpha }^2{x}^2\alpha x}{1}\end{array}$

$\begin{array}{cc}\Rightarrow {\alpha }^3=\frac{1}{x^3}& \Rightarrow \alpha =\frac{1}{x}\\ & \text{or}\alpha x=1\\ \text{using in}\left(1\right):x-2& =1\Rightarrow x=3\end{array}$