Question

In which of the following reactions, the equilibrium constant will be unitless?

• A. $H_2\left(g\right)+l_2\left(g\right)\rightleftharpoons 2HI\left(g\right)$
• B. In all the above reactions
• C. $NO\left(g\right)\rightleftharpoons \frac{1}{2}{N}_2\left(g\right)+\frac{1}{2}{O}_2\left(g\right)$
• D. $CO\left(g\right)+H_{2}O\left)\right(g)\rightleftharpoons C{O}_2(g)+H_2(g)$

Answer 1

The correct option is B In all the above reactions

For a general reaction
$aA+bB\to cC+dD$
Equilibrium constant is written as:
$\Rightarrow K_c=\frac{\left|C^c\right|\left|D^d\right|}{{\left|A\right|}^a{\left|B\right|}^b}$
so, whenever total moles of reactant and that of products are same i.e $(\Delta n_g=0)$, $K_c$ will have no units which hold true for all the reactions here (since all the species are in gaseous phase only).