The Foundations of Chemistry

We see that H
is a reactant in step 1, but it is completely regenerated in step 5. H


is therefore a catalyst. The species shown in brackets in steps 1 through 4 are reaction

intermediates.Ethyl acetate and water are the reactants, and acetic acid and ethanol are

the products of the overall catalyzed reaction.

Heterogeneous Catalysis

A heterogeneous catalyst(also known as a contact catalyst) is present in a different

phase from the reactants. Such catalysts are usually solids, and they lower activation ener-

gies by providing surfaces on which reactions can occur. The first step in the catalytic

process is usually adsorption,in which one or more of the reactants become attached to

the solid surface. Some reactant molecules may be held in particular orientations, or some

bonds may be weakened; in other molecules, some bonds may be broken to form atoms

or smaller molecular fragments. This causes activationof the reactants. As a result, reac-

CH 3 C OCH 2 CH 3

O

H
 CH 3 C OCH 2 CH 3

OH

CH 3 C OCH 2 CH 3 
H 2 O C

O


H H

CH 3 OCH 2 CH 3

OH OH

step 1

CH 3 C OH HOCH 2 CH 3

OH

OH

step 4

step 5

overall

step 2

CO step 3

HO

CH 3 CH 2 CH 3

OH

H

C

O


H H

CH 3 OCH 2 CH 3

OH

CO

HO

CH 3 CH 2 CH 3

OH

H

ethanol

CH 3 C OH H

O

CH 3 C OH 


acetic acid

CH 3 C OCH 2 CH 3

O

H 2 O

H



 CH 3 CCHOH 3 CH 2 OH

O

ethyl acetate acetic acid ethanol

Groups of atoms that are involved in
the change in each step are shown in
blue. The catalyst, H
, is shown in
red.

690 CHAPTER 16: Chemical Kinetics

The petroleum industry uses numerous heterogeneous catalysts. Many of them contain

highly colored compounds of transition metal ions. Several are shown here.

All intermediates in this sequence of
elementary steps are charged species,
but this is not always the case.