Pseudo-First-Order Reaction
A higher-order reaction that behaves as first order because one reactant is present in such large excess that its concentration is effectively constant.
Formula / equation
rate = k′[A], k′ = k[B]₀
Unit
s⁻¹
In depth
Flooding the system with one reagent collapses a complicated rate law into a simple exponential decay, which makes the data far easier to analyse. Repeating the experiment at several excess concentrations then recovers the true order with respect to the flooded species.
Examples in the real world
Ester hydrolysis in dilute aqueous solution, where water is present at about 55 M and barely changes.