Equilibrium concentrations and Kc

Dinitrogen tetroxide dissociates into nitrogen dioxide: $\mathrm{N_2O_4(g) \rightleftharpoons 2NO_2(g)}$. A chemist seals 0.500 mol of $\mathrm{N_2O_4}$ in a flask of volume 2.00 $\mathrm{dm^3}$ and holds it at a constant temperature. At equilibrium the flask contains 0.140 mol of $\mathrm{NO_2}$.

A student mixes 1.00 mol of ethanoic acid with 1.00 mol of ethanol and a few drops of acid catalyst, and leaves the mixture to reach equilibrium: $\mathrm{CH_3COOH(l) + C_2H_5OH(l) \rightleftharpoons CH_3COOC_2H_5(l) + H_2O(l)}$. At equilibrium the mixture contains 0.667 mol of ethyl ethanoate.

Hydrogen and iodine react in a sealed flask: $\mathrm{H_2(g) + I_2(g) \rightleftharpoons 2HI(g)}$. At the temperature used, $K_c = 49.0$. The flask initially contains 1.00 mol of $\mathrm{H_2}$ and 1.00 mol of $\mathrm{I_2}$.

Sulfur trioxide forms in the equilibrium $\mathrm{2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)}$.

Iron(III) ions and thiocyanate ions form a deep red complex: $\mathrm{Fe^{3+}(aq) + SCN^-(aq) \rightleftharpoons FeSCN^{2+}(aq)}$. A student mixes 10.0 $\mathrm{cm^3}$ of 0.0020 $\mathrm{mol\,dm^{-3}}$ $\mathrm{Fe^{3+}}$ with 10.0 $\mathrm{cm^3}$ of 0.0020 $\mathrm{mol\,dm^{-3}}$ $\mathrm{SCN^-}$. A colorimeter shows that at equilibrium $[\mathrm{FeSCN^{2+}}] = 3.0 \times 10^{-4}\ \mathrm{mol\,dm^{-3}}$.