Chapter 14, Problem 14.110QP

Gaseous acetic acid molecules have a certain tendency to form dimers. (A dimer is a molecules formed by the association of two identical, simpler molecules.) The equilibrium constant K_p at 25°C for this reaction is 1.3 × 10³.

1. a If the initial pressure of CH₃COOH monomer (the simpler molecule) is 7.5 × 10⁻³ atm, what are the pressures of monomer and dimer when the system comes to equilibrium? (The simpler quadratic equation is obtained by assuming that all of the acid molecules have dimerized and then some of it dissociates to monomer.)
2. b Why do acetic acid molecules dimerize? What type of structure would you draw for the dimer?
3. c As the temperature decreases, would you expect the percentage of dimer to increase or decrease? Why?