## pseudo first order

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

inlovewithchemistry
Posts: 104
Joined: Fri Sep 28, 2018 12:19 am

### pseudo first order

what is the cut off for something to be considered "very large" for pseudo first order? how will we know to do this? i dont have a full understanding fo the process.

timothy_ho_4B
Posts: 61
Joined: Fri Sep 28, 2018 12:29 am

### Re: pseudo first order

I'm pretty sure that the question will state that one is obviously "very large" or in excess so that a pseudo first order reaction can be conducted.

Angel Chen 2k
Posts: 59
Joined: Fri Sep 28, 2018 12:20 am

### Re: pseudo first order

Pseudo rate laws are generated because rate laws cannot be used for reactions with more than one reactant since changes in both reactants, most of the times, occur simultaneously. With Pseudo rate laws, the concentration of one reactant must be in large excess ( so the concentration is essentially constant and unchanging). So to answer your question, as long as the concentration is large enough so that the change is not significant to change the concentration itself, then it would be considered as "very large".