The equilibrium N2O4 (g) -->--< 2NO2 (g) is set up when N2O4 dissociates. When 0.0370 moles of N2O4 dissociates at 25 degrees in a 0.5dm3 sealed container, 0.0310 moles of N2O4 remains at equilibrium. Calculate the value of Kc for this reaction.

The first step is to formulate the Kc expression. Kc is the "concentration of the products / concentration of the reactants". We show concentration is in moldm^-3 by using square brackets. The molar co-efficient in the equation are the powers. So, here Kc would be: Kc = [NO₂]² / [N₂O₄]. This style of calculation is best with a SUE table with S being the starting moles, U being the moles used and E being the moles at equilibrium. N₂O₄: Starting moles, 0.0370. Used moles, -0.006. End moles, 0.0310.NO₂: Starting moles, 0. Used moles, +0.012. End moles, 0.0120.These are the number of MOLES at equilibrium, but for Kc we need concentration. c=n/v, so we simply divide by the volume (0.5dm^-3) to get concentrations of N2O4: 0.0620 and NO2: 0.0240. Substitute into the Kc expression we constructed before and Kc turns out to be: (0.0242)/(0.0620) = 9.29X10-3 to 3sf. Final step is to work out the units, which turn out to be simply moldm^-3.