The hydrolysis of methyl acetate in water, CH_3COOC_2H_5(aq) + H_2O(l) rightarro

Question

The hydrolysis of methyl acetate in water, CH_3COOC_2H_5(aq) + H_2O(l) rightarrow CH_3 COOH(aq)^+ C_2H_2OH(aq), is pseudo-first order in dilute aqueous solutions with a rate constant of 2.00 times 10^-3 min^-1. What is the value of the second-order rate constant, where the concentration of water is no longer assumed to be 55.5 M? The rate at which gas-phase hydrogen and iodine react to form hydrogen iodide, H_2(g) + I_2(g) rightarrow 2 HI(g) can be increased by using a platinum catalyst. Suppose the uncatalyzed reaction has an activation energy of about 180 kJ, while that of the catalyzed reaction is about 60 kJ at 600 K. Approximately how many times faster is the catalyzed reaction relative to the uncatalyzed? Assume the frequency factor is the same for both processes.

Explanation / Answer

1.

pseudo order rate constant K = K’CA

K = rate constant = 2*10-5/min and CA= 55.5M

K’ = K/CA= 2*10-5/min/55=3.64*10-7 /M.min

2. From Arhenius equation

ln (K2/K1)= 1/RT*(Ea1-Ea2)

where K2= rate constant for catalyzed reaction and K1= rate constant for uncatalyzed reaction

Ea= activation energy , R= 8.314 J/mole.K

ln(K2/K1)= (180-60)*1000/(8.314*600)= 24

K2/K1= 2.8*1010 times

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