Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

2.5 Kinetics of third-order reactions 28
2.5 Kinetics of third-order reactions
y
A+B+C→ D (2.98)
− [A]
= [A] [B] [C] (2.99)
I Pseudo second-order combination reactions: In combination reactions of two
species A + A → A 2 or A + B → AB (for example, the recombination of two free
radicals), one of the species (bath gas M) is usually present in large excess ([M] À [A],
[B]), so that the kinetics becomes pseudo second-order, giving the two cases:
•
•
A+A+M→ A 2 +M (2.100)
A+B+M→ AB + M (2.101)
M plays the role of an inert collision partner which removes the excess energy from the
newly formed A 2 or AB molecules.