In the gas phase, acetic acid exists as an equilibrium of monomer and dimer mole

Question

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 equilibriurn constant, Ke , at 25 °C for the monomer-dimer equilibrium has been determined to be 3,.2 x 10. Assume that acetie acid is present initially at a concentration of 7.3 x 10 moll, at 25 °C and that no dimer is present initially Increasing the temperature will shift the equilibrium to the left. Increasing the temperature will shift the equilibrium to the right. No shift will occur

Explanation / Answer

            2 CH3COOH <===> (CH3COOH)2

initial   (7.3*10^-4) M           0 M

change       -2x                   x M

equili    (7.3*10^-4)-2x           x M

    Kc = [(CH3COOH)2]/[CH3COOH]^2

(3.2*10^4) = x/((7.3*10^-4) -2x)^2

x = 3.15*10^-4

concentration of CH3COOH remained = 7.3*10^-4 -2x

                                    = (7.3*10^-4) -(2*3.15*10^-4)

                                     = 1*10^-4 M

percentage of aceticacid converted to dimer = (1*10^-4)/(7.3*10^-4)*100

          = 13.7%

b) as H-bond formation is an exothermic process, low temperature is favourable.so that, increasing temperature decreases formation of H-bond

   answer: Increasing the temperature will shift the equilibrium to the left.

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