Question

A chemist interested in the reactivity of iodine concentrates his study on the decomposition of gaseous hydrogen iodide (Reaction 1).

$2HI\left(g\right)\leftrightharpoons H_2\left(g\right)+I_2\left(g\right)$
What is the equilibrium expression for Reaction 1?

• A. ${\left[H_2\right]}^2\left[I_2\right]$
• B. $\left[H_2\right]$
• C. $\left[H_2\right]\left[I_2\right]/{\left[HI\right]}^2$
• D. $\left[H_2\right]{\left[I_2\right]}^2$

Answer 1

The correct option is C $\left[H_2\right]\left[I_2\right]/{\left[HI\right]}^2$

The equilibrium constant of a reaction is the ratio of the products to its reactants both raised to the power of its coefficient.

Hence, $K_c=\frac{\left[H_2\right]\left[I_2\right]}{[HI{]}^2}$