Consider the following simple combination reaction: 2AA2. (a) Suppose the reacti
ID: 884416 • Letter: C
Question
Consider the following simple combination reaction: 2AA2.
(a) Suppose the reaction is first order in [A]. If the rate constant is k = 1.0 x 106 s-1,
what is the time required for the concentration of [A] to decrease from 1.0 M
initially down to 0.10 M? (Note: the reaction stated in this part is not elementary.)
(b) Now, suppose the reaction is second order in [A]. If the rate constant is k =
1.0 x 106 L mol-1 s-1, what is the time required for the concentration of [A] to
decrease from 1.0 M initially down to 0.10 M?
(c) Based on your results in parts (a) and (b), which order of reaction leads to a faster
decrease to one tenth of the initial concentration? On the same graph, sketch a plot
of [A(t)] versus t, where t is time, for both first order (solid line) and second order
(dashed line) reactions of parts (a) and (b).
Explanation / Answer
A) first order K = 2.303/t log(a/a-x)
1.0*10^6 = 2.303/tlog(1/0.1)
= 2.303*10^-6 sec
b) K = 1/t[1/(a-x)-1/a]
1.0*10^6 = 1/t((1/0.1)-1)
t = 9*10^-6 sec
fro the data reaction is faster in first order.