[slu1986]

For a particular first-order reaction, it takes 48 minutes for the concentration of the reactant to decrease to 25% of its initial value.  What is the value for rate constant in (s^-1) for the reaction?

A) 1.0 * 10^-4 s^-1
B) 4.8 * 10^-4 s^-1
C) 6.0 * 10^-3 s^-1
D) 2.9 * 10^-2 s^-1

This question is throwing me off when tells the time that it takes the concentration to decrease to 25% of its initial value.  I know that the problem has something to do with half life...I just don't know how to set up the formula to solve for the value of the rate constant.  Could someone please guide me in the right direction? I would appreciate it.   

[Astrokel]

hello,

you have to show your work!

do you know the formula t_1/2 = (ln2)/k for first order reaction?

Now you just have to find the half-life. Consider this decay,

         t_1/2         t_1/2           t_1/2
100% ---> 50% ----> 25% ---->

hope this helps some