Environmental scientists calculating pollutant half-lives often define a transpo
ID: 955524 • Letter: E
Question
Environmental scientists calculating pollutant half-lives often define a transport rate constant that is analogous to a reaction rate constant and describes how a pollutant moves out of an ecosystem. In a study of the gasoline additive MTBE in Donner Lake, California, scientists from the University of California, Davis, found that in the summer the half-life of MTBE in the lake was 23 days. Assume that the transport process is first order. What was the transport rate constant of MTBE out of Donner Lake during the study? Express your answer in reciprocal days. Experimental evidence shows that in the reaction NO_2(g) + CO(g) rightarrow NO(g) + CO_2(g) the reaction rate depends only on the concentration of NO_2. Determine whether the reaction is first or second order in NO2, and calculate the rate constant from the data obtained at 488 K in the table below. Concentration of NO_2 as a Function of Time The reaction is first order. The reaction is second order. The rate constant isExplanation / Answer
5 )
half life = 23 days
rate constant = 0.693 / half life = 0.693 / 23 =0.0301 days-1
rate constant = 0.0301 days-1
6)
test out for second order reaction
rate constant = k = 1/t [1 /At- 1/ Ao]
Ao -----------> initial concentration
At ------------> concentration after t time
now from data :
at 1.39 hours
k = 1/ 1.39 [ 1/ 0.198 - 1/ 0.250 ]
k = 0.76 M-1 h-1
at 3.06 hours
k = 1/ 3.06 [ 1/ 0.159 - 1/ 0.250 ]
k = 0.76 M-1 h-1
at 4.72 hours
k = 1/ 4.72 [ 1/ 0.132 - 1/ 0.250 ]
k = 0.76 M-1 h-1
so in all cases rate constant value is constant for secon order.
so it is second order reaction
rate constant = 0.76 M-1 h-1
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