## Key Words for First Order Reactions Half Life Problems

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

Silvino Jimenez 1A
Posts: 52
Joined: Fri Sep 29, 2017 7:04 am

### Key Words for First Order Reactions Half Life Problems

I am having a hard time identifying the order of a reaction given half life reaction time t1/2.

Are there key words or phrases that indicate a reaction is first order when determining half life reaction time?

lizzygaines1D
Posts: 52
Joined: Thu Jul 13, 2017 3:00 am

### Re: Key Words for First Order Reactions Half Life Problems

Usually the question will give you the order, and if it doesn't it should give the units of k. If the units are inverse time units, you'll know its first order etc. etc.

Brigitte Phung 1F
Posts: 50
Joined: Thu Jul 27, 2017 3:00 am
Been upvoted: 1 time

### Re: Key Words for First Order Reactions Half Life Problems

I also believe the problems should always tell you the order of the reaction as 23, 25, 27, and many others also do. But in the case they don't, you can always check the units of k!
- zero-order: k is in units of mol * L^-1 * s^-1
- first-order: k is in units of s^-1
- second-order: k is in units of L * mol^-1 * s^-1

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