Only the collision in Figure 16-9a is in the correct orientation to transfer an oxygen atom
from the linear N 2 O molecule to form the angular NO 2 molecule. For some reactions,
the presence of a heterogeneous catalyst (Section 16-9) can increase the fraction of
colliding molecules that have the proper orientations.
TRANSITION STATE THEORY
Chemical reactions involve the making and breaking of chemical bonds. The energy asso-
ciated with a chemical bond is a form of potential energy. Reactions are accompanied by
changes in potential energy. Consider the following hypothetical, one-step reaction at a
certain temperature.
16-6
Figure 16-9 Some possible
collisions between N 2 O and NO
molecules in the gas phase. (a) A
collision that could be effective in
producing the reaction. (b, c)
Collisions that would be ineffective.
The molecules must have the proper
orientations relative to one another
andhave sufficient energy to react.16-6 Transition State Theory 677Ineffective
orientation
of collisionIneffective
orientation
of collisionEffective
orientation
of collisionProductsReaction
occursReactants CollisionReactants CollisionReactants CollisionReactantsReactantsNo reactionNo reactionNO + N 2 O → NO 2 + N 2
(a)(b)(c)See the Saunders Interactive
General Chemistry CD-ROM,
Screen 15.10, Microscopic View of
Reactions (2): Transition State Theory.