### 15.35

Posted:

**Tue Feb 21, 2017 1:17 am**"The half-life for the second order reaction of a substance A is 50.5 s when [A]naught=0.84 M. Calculate the time needed for concentration of A to decrease to a) one sixteenth, b) one-fourth, c) one-fifth it's original value."

For this question, after looking at the solutions manual, I could pretty easily see the pattern of what you're supposed to do. For example, for a) you would write:

T= (16/[A]naught - 1/[A]naught) / k

What I don't understand, however, is why this equation works, and why you would write the equation this way.

If anyone could explain this I would much appreciate it.

Thank you!

For this question, after looking at the solutions manual, I could pretty easily see the pattern of what you're supposed to do. For example, for a) you would write:

T= (16/[A]naught - 1/[A]naught) / k

What I don't understand, however, is why this equation works, and why you would write the equation this way.

If anyone could explain this I would much appreciate it.

Thank you!