Ethanoic acid (acetic acid) can dimerize in the gas phase according to the equilibrium
2CH3COOH(g)⇌(CH3COOH)2(g)
At 450 K the equilibrium constant for this dimerization is Kc=7.8×10−2. A researcher injects 2.0×10−2mol of gaseous ethanoic acid into an evacuated 5.00 L flask and allows the system to reach equilibrium at 450 K.
(1) Based solely on the magnitude of Kc, predict whether monomeric ethanoic acid or the dimer will predominate at equilibrium. Justify your prediction qualitatively.
(2) Assuming ideal-gas behavior, calculate the initial concentration of ethanoic acid monomer in the flask before any dimerization occurs.
(3) Using an appropriate approximation grounded in the magnitude of Kc, estimate the equilibrium concentration of the dimer. State and justify any assumptions made to simplify the calculation.
(4) Express the percentage of total ethanoic acid molecules that exist as the dimer at equilibrium under these conditions.