CH 2
CH 2
CH 2
CH 2
H
Gly
193
Ser
195
Asp
102
His
57
O
O
C
O
H C
HC
NH CH
O N
N
H
HN N
A
catalystis a substance that increases the rate of a
chemical reaction without itself being consumed or changed
in the reaction. We have seen that the rate of a chemical reaction depends on
the energy barrier that must be overcome in the process of converting reactants into
products (Section 3.7). The height of the “energy hill” is indicated by the free energy
of activation A catalyst increases the rate of a chemical reaction by providing a
pathway with a lower
A catalyst can decrease in one of three ways:
- The catalyzed and uncatalyzed reactions can follow different, but similar, mecha-
nisms, with the catalyst providing a way to convert the reactant into a less stable
species(Figure 24.1a).
- The catalyzed and uncatalyzed reactions can follow different, but similar, mecha-
nisms, with the catalyst providing a way to make the transition state more stable
(Figure 24.1b).
¢G‡
¢G‡.
(¢G‡).
24
Catalysis
999
∆G‡uncatalyzed
Free energy
Progress of the reaction
∆G‡catalyzed
b.
∆G‡uncatalyzed ∆G‡catalyzed
Free energy
Progress of the reaction
a.
Figure 24.1
Reaction coordinate diagrams for an uncatalyzed reaction and for a catalyzed reaction. (a) The catalyst converts the
reactant to a less stable species. (b) The catalyst stabilizes the transition state.
