## Half-Lives

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

David Sarkissian 1K
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### Half-Lives

Are we suppose to ignore the half-life formulas for zero-order and second-order reactions? The textbook mentioned that we only ever really use the half-life equation of a first-order reaction, but all three formulas are on our formula sheet.

Michelle Wang 4I
Posts: 63
Joined: Fri Sep 28, 2018 12:27 am

### Re: Half-Lives

No, it is possible that we could be asked to calculate the half life of zero or second order reactions. You just have to be careful because unlike with first order reactions, the inital/starting concentration changes the half life. So for each starting concentration there is a different half life.

mbaker4E
Posts: 69
Joined: Fri Sep 28, 2018 12:26 am

### Re: Half-Lives

Yes, you should definitely know how to use all the half-life equations because they are different for every order and can sometimes be useful in finding k.

Ronald Thompson 1F
Posts: 59
Joined: Fri Sep 28, 2018 12:25 am

### Re: Half-Lives

Yes it is useful to know how to use them.

Mona El Masri 1F
Posts: 34
Joined: Fri Sep 28, 2018 12:20 am

### Re: Half-Lives

If its on the formula, you most likely will need to know it/use it. Good luck!