## Calculating Half-life

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

Anaranjo
Posts: 14
Joined: Wed Nov 18, 2015 3:00 am

### Calculating Half-life

At 500°C cyclopropane (C3H6) rearranges to propene (CH3CHCH2). The reaction is first-order with a rate constant of 6.7×10-4 s-1. What is the half-life of the reaction at 500C?

Andrew Nguyen 3G
Posts: 22
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Calculating Half-life

t1/2 for first order reactions is .693/k or .693 / 6.7×10-4 s-1

t1/2 = 1034.32 seconds, or 1000 seconds for significant figures.

Julia Hwang 3G
Posts: 22
Joined: Wed Sep 21, 2016 3:00 pm

### Re: Calculating Half-life

A tip to know when to use which equation is to look at what you're given. Since the initial and final concentrations are not mentioned, you can infer that the equation t1/2 = 0.693/k is what you need to use to find the half life.