First Order vs Pseudo First Order

[laurence14b2f]

Hi all! How do we distinguish between a first-order reaction and a reaction that appears to follow pseudo-first-order kinetics? Thank youuu

[005917072]

A pseudo-first-order reaction is part of a second order reaction that has multiple reactants, but if all but one reactants are in great excess then the reaction will seem to only depend on that one reactant with a lower concentration (since all the other reactants will stay constant), making it seem like a first order reaction. And then an actual first order reaction is when the reaction actually just depends on the concentration of one reactant, so rate = k[A].

[Chris_1234]

A first-order reaction's rate depends only on one reactant's concentration, following the formula Rate = k[A]. In contrast, a reaction with pseudo-first-order kinetics seems like a first-order reaction, but it's because one reactant is in much higher amounts, making the rate appear to depend only on the other reactant's concentration, following the formula Rate = k'[B].