## half life equation

$aR \to bP, Rate = -\frac{1}{a} \frac{d[R]}{dt} = \frac{1}{b}\frac{d[P]}{dt}$

Belle Calforda3f
Posts: 67
Joined: Fri Sep 29, 2017 7:07 am

### half life equation

does a half life pertain to a substance in general or an AMOUNT of substance? for ex: does mercury have one half life or do different amounts of mercury have different half lives?

Vasiliki G Dis1C
Posts: 53
Joined: Fri Sep 29, 2017 7:04 am

### Re: half life equation

It depends on if the reaction is zero order, first, or second. The zero order half life equation is [A]o/2k, and depends on the initial amount of the substance you have. For example, it would depend on the initial concentration of mercury you have, and would vary depending on that concentration. For first order reactions, the half life equation is 0.693/k, and is independent of the concentration, so it is the same for that substance regardless of how much you initially have. So, the half life for a first oder reaction of mercury would be the same no matter the initial concentration. For second order reactions, the equation is 1/k[A]o, so it does depend on the initial concentration in the same way as the zero order reaction. Hope this helps!