Chapter 15, Problem 48GQ

In the gas phase, acetic acid exists as an equilibrium of monomer and dimer molecules. (The dimer consists of two molecules linked through hydrogen bonds.)

The equilibrium constant, K_c, at 25 °C for the monomer-dimer equilibrium

2 CH₃CO₂H ⇄ (CH₃CO₂H)₂

has been determined to be 3.2 × 10⁴. Assume that acetic acid is present initially at a concentration of 5.4 × 10⁻⁴ mol/L at 25 °C and that no dimer is present initially.

(a) What percentage of the acetic acid is converted to dimer?

(b) As the temperature increases, in which direction does the equilibrium shift? (Recall that hydrogen-bond formation is an exothermic process.)