Summary Transition metals

② HOMOGENEOUS CATALYSTS
· These work by forming intermediates to provide an alternate reaction pathway with a lower Ea
· The intermediate species reacts to form the products , and reforms the catalyst -




·
Homogeneous Catalysts have a unique energy profile diagram
.
Homogeneous energy profiles
have 2 activation energies !

A
------------- = Activation energy with
No
Catalyst
------------- ------




~
-




-------------------- - = Activation
energy
with
A Catalyst -
1st step-



/
- -
- -
h - -




REACTANTS
& =
Activation energy with
catalyst 2nd stes
-




·
Intermediates are
formed at this point . ↳
The lowers the
catalyst
activation energy so

PRODUCTS more particles have

to react.
enough energy



⑭
REACTION PROGRESS




EXAMPLE HOMOGENEOUS CATALYST factions
Of
-
Catalysed by
↳ REACTION BETWEEN IODIDEIONS AND PEROXODISULFATE IONS

· The reaction uncatalysed is very slow .
We are trying to react two negatively charged ions together , which

REPEL .
As a result ,
this reaction has a high activation energy
.


enal catalyst
250 +"
S20gag + 2
l jag >
[2caq) +
ag)



This occurs in 2 stages :




Oxidised
CATALYST -
Fet catalyst lowers Ea and speeds us

① 3 c 08
ag
+
2fecass >
- 25est
(ag)
+ 250 , caa)
reaction
. Peroxodisulfate is REDUCED

- INTERMEDIATE

reduced



2 fet
② Ife lag +
21 jag) >
-
Ezcag) +
(aq)
Fest intermediate reacts with iodide ions
INTERMEDIATE CATALYST
REFORMED
to produce !2 - felt is REFORMED



↓
TEST FOR IODINE : Starch solution turns blue-black in presence of J2 .