Question

What is the equilibrium concentration of each of the substances of RHS in the equilibrium when the initial concentration of ICl was 0.78 M?
$2ICl\left(g\right)\rightleftharpoons I_2\left(g\right)+C{l}_2\left(g\right);K_C=0.25$ :

• A. 0.195 M
• B. 0.42 M
• C. 4.2 M
• D. 2.1 M

Answer 1

The correct option is A 0.195 M

The equilibrium reaction is $2ICl\left(g\right)\rightleftharpoons I_2\left(g\right)+C{l}_2\left(g\right);K_C=0.25$.
Let x represents the equilibrium concentration of iodine.
It is also equal to the equilibrium concentration of chlorine.

	ICl	$I_2$	$C{l}_2$
Initial	0.78	0	0
Change	-2x	x	x
Equilibrium	0.78-2x	x	x

The expression for the equilibrium constant is $K_C=\frac{\left[I_2\right]\left[C{l}_2\right]}{\left[ICl\right]}$.
Substitute values in the above expression.
$0.25=\frac{x^2}{(0.78-2x{)}^2}$
Thus $x=0.195M$.
Hence, the option A is the correct answer.