Equilibria-kc Question 3

\begin {aligned}

2HI_{(g)}\rightleftharpoons H_{2(g)}+I_{2(g)}

\end {aligned}

The following equilibria was found to contain 3 moles of HI, 6 moles of H₂ and 1 mole of I₂.

Find  K_c.

In such a question the first thing to write is the k_c equation:

\begin {aligned}

k_c=\frac{[H_2][I_2]}{[HI]^2}

\end {aligned}

Since the moles given are all at equilibrium, then it is not necessary to write the ICE table.

Since the volume is not given, this is taken as V. This makes the concentration of each items to:

\begin {aligned}

[HI]=\frac{3}{V}

\end {aligned}

\begin {aligned}

[I_2]=\frac{1}{V}

\end {aligned}

\begin {aligned}

[H_2]=\frac{1}{V}

\end {aligned}

Once the concentrations are found, then it is just a matter of placing each value in the k_c equation as follows:

\begin {aligned}

k_c=\frac{(\frac{3}{V})^2}{(\frac{6}{V})(\frac{1}{V})}

\end {aligned}

Since all the Volume can cancel out, then k_c can be found as 1.5.