## pseudo vs 2nd order

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

Vanessa Reyes_1K
Posts: 60
Joined: Fri Sep 28, 2018 12:28 am

### pseudo vs 2nd order

When is it appropriate to use the pseudo 1st order for a reaction?

Amy Lefley 1J
Posts: 60
Joined: Fri Sep 28, 2018 12:15 am

### Re: pseudo vs 2nd order

It is appropriate to use pseudo-first order rate law when all reactant concentrations are changing, making the reaction very difficult to study. In this case, we make one reactant concentration small and the others large so that the reaction rate is dependent on only one reactant.

Linh Vo 2J
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Joined: Sat Apr 28, 2018 3:00 am

### Re: pseudo vs 2nd order

To add, in discussion, my TA told me it's appropriate to use it when n=1.

Dimitri Speron 1C
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Joined: Fri Sep 28, 2018 12:17 am
Been upvoted: 1 time

### Re: pseudo vs 2nd order

You can use the pseudo especially when your rate law is dependent on multiple reactants. If the reaction is first order with respect to any of them it can be rewritten as pseudo-first order.

Sophia Ding 1B
Posts: 62
Joined: Fri Sep 28, 2018 12:16 am

### Re: pseudo vs 2nd order

Is it safe to assume that we'll always be told which reactants will be in large excess to us to be able to write the pseudo rate law?