72. The reaction (CH),CBr + OH-_ (CH),COH + Br- in a certain solvent is first or

Question

72. The reaction (CH),CBr + OH-_ (CH),COH + Br- in a certain solvent is first order with respect to (CHs)CBr and zero order with respect to OH. In several experiments, the rate constant k was determined at different temperatures. A plot of In(k) versus 1/T was constructed resulting in a straight line with a slope value of-1.10 × 104 K and y-intercept of 33.5. Assume k has units of s1. a. Determine the activation energy for this reaction. b. Determine the value of the frequency factor A. c. Calculate the value of k at 25°C.

Explanation / Answer

Arhenius equation can be written as

lnK= lnKo-Ea/RT, where Ko is frequency factor and T is temperature in K and Ea is activation energy and R is gas constant, R= 8.314 J/mole.K

K is rate constant. So a plot of lnK vs 1/T gives the slope of -Ea/R

given the slope is -Ea/R= -1.1*104, Ea= 1.1*104*8.314 J/mole.=91454 J/mole

intercept is noting but lnKo= 33.5, Ko =exp(33.5)= 3.54*1014

hene the Arhenius equation is lnK= 33.5-1.1*104/T

at 25 deg.c, T= 25+273= 298 K

lnK= 33.5-1.1*104/298, K=0.03295/sec

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