Posted by **mandy** on Monday, May 3, 2010 at 9:44pm.

10% of a sample reacts in 25 s. If the reaction follows first order kinetics, how long would it take for half the sample to react?

- Chemistry -
**DrBob222**, Monday, May 3, 2010 at 10:20pm
ln(No/N) = kt

If we start with an arbitrary number, say 100, and 10% is used, that would leave 90

ln(100/90) = k(25sec)

solve for k. You want the half life; therefore, substitute the k you find in the same equation but this time start with 100 and N = 50 (half is gone). Solve for t and that will be t_{1/2}

- Chemistry -
**Anonymous**, Friday, March 22, 2013 at 12:17am
Ei

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