Question

The decomposition reaction, X → products, has rate constant k = 0.00437 mol−1 L s−1. How long will it take for the decomposition to be 75% complete, if the initial concentration of X is 1.85 mol L−1 ?

Answer 1

got 423s by doing ln(.25)(1.85)/0.00437, but thats wrong

Answer 2

I couldn't pull up the second link. From what you have written here I think you must have used a first order equation. From a scare glimpse I think this is a second order equation so put the date into the integrated form of a second order and try that.

Answer 3

how do you know that this is a second order equation?

Answer 4

From the units. The units are different for zero, first, second, third order etc. Pull up Google, look at Wikipedia. They tell you the units for which order.
For second order that is 1/A + 1/Ao = kt

Answer 5

hmm still not getting the right ans. i did (1/.25 - 1/1.85)1/.00437. what am i doing wrong?

Answer 6

I think we goofed. I wrote the equation wrong. It should be
1/[A] - 1/([A]o = kt.
Second, from the problem [A]o = 1.85. But [A] = 1.85*0.25 = 0.4625
Try that.