[kimi85]

A reaction is 50% complete in 30.0 min.  How long after its start will the reaction be 75% complete if it is  a . first order  b. zero order?

I used the formula for the first order reaction and also for the zero order reaction. I first solved for the reaction constant. Then used it for the reaction which is 75% complete. But I don't get the correct answer.

Here's what I did:

ln 0.5 = -k (30 min), ln 0.75 = -k(t). I solved for t

The correct answers are 60 min and 45 min for first order and 2nd order, respectively.

Thank you very much!

[Yggdrasil]

If the reaction is 75% complete that means that 25% remains and the equation you would want to solve is:

ln(0.25) = -kt

[kimi85]

Thank you.