1.11- The effects of Cat. on Ea
1.12 The Effect of Cat. on RM
1.13 Some uses of Cat.
• compare the PE diagrams for a catalyzed and uncatalyzed
reaction in terms of:
– activated complex
– reaction intermediates
– reaction mechanism
– activation energy
• identify platinum in automobile catalytic converters as a catalyst
• describe the effect of a catalyst on a number of reactions, such
– decomposition of hydrogen peroxide (catalysts: manganese (IV) oxide,
raw liver, raw potato)
– the reaction of the oxalate ion with acidified potassium permanganate
solution (catalyst: Mn2+)
– the decomposition of bleach (catalyst: cobalt (II) chloride)
CATALYSTS SPEED IT UP
• A catalyst is like adding a bit of magic to a
• Reactions need a certain amount of energy
to happen. If they don't have it, oh well, the
reaction probably can't happen.
• A catalyst lowers the amount of energy
needed so that a reaction can happen
• A catalyst is about energy; it doesn't have to
be another molecule.
– If you fill a room with hydrogen gas and oxygen
gas, very little will happen. If you light a match in
that room (or just a spark), all of the hydrogen and
oxygen will combine to create water molecules. It
is an explosive reaction.
• The energy needed to make a
reaction happen is called the
• As everything moves around,
energy is needed.
• The energy a reaction needs is
usually in the form of heat.
• When a catalyst is added,
something special happens.
– Maybe a molecule shifts it's
– Maybe that catalyst makes two
molecules combine and they
release a ton of energy. That
extra energy might help another
reaction to occur. In our earlier
example, the spark added the
The Effects of Catalysts
• Earlier we defined a catalyst as a substance that
speeds up a reaction. Let’s refine that definition a
• CATALYST: a substance which provides an overall
reaction with an alternative mechanism having lower
• Catalysts provide an alternative pathway by inserting
different intermediate steps and lowering the activation
energy for the reaction to occur. ∆H is not changed,
but the “energy hump’ is lowered.
• Since the activation energy is lowered, a
greater fraction of reactant molecules will have
sufficient KE to form the activated complex.
Since more reactant molecules can react in a
certain time, the forward reaction rate
REACTANTS ↔ PRODUCTS
• By lowering the “energy hump” for the forward
reaction, we have also lowered it for the reverse
• Since a greater fraction of product molecules will have
sufficient KE to form the activated complex, the
reverse reaction rate increases also.
If the forward reaction rate doubles, the reverse reaction
rate also doubles.
Let’s examine a “real life” example
• The decomposition of formic acid has been
extensively studied. At room temperature, the reaction
is very slow with no noticeable activity. As soon we
acidify the solution with sulfuric acid, the solution
begins to bubble
What is happening?
• Some important things to remember about catalysts:
– The catalyst is an active participant in a reaction which is
regenerated in a later step of the reaction mechanism.
– ∆H for the overall reaction is the same for both the catalyzed
and un-catalyzed reaction; only the intermediate reactions
– All intermediates and catalysts cancel out when the
individual steps are added up to get the overall reaction.
Catalysis' and activation energy
2 H2O2 ---> 2 H2O + O2
Uses of Catalysts
• Estimates are that 90% of all commercially
produced chemical products involve
catalysts at some stage in the process of
• In 2005, catalytic processes generated
about $900 billion in products worldwide.
• Petroleum refining makes intensive use of catalysis for alkylation, catalytic cracking
(breaking long-chain hydrocarbons into smaller pieces), naphtha reforming, steam
reforming (conversion of hydrocarbons into synthesis gas). Even the exhaust from
the burning of fossil fuels is treated via catalysis: Catalytic converters, typically
composed of platinum and rhodium, break down some of the more harmful
byproducts of automobile exhaust.
2 CO + 2 NO → 2 CO2 + N2
• With regards to synthetic fuels, an old but still important process is the Fischer-
Tropsch synthesis of hydrocarbons from synthesis gas, which itself is processed via ,
catalysed by iron. Biodiesel and related biofuels require processing via both
inorganic and biocatalysts.
• Fuel cells ( Unit 5) rely on catalysts for both the anodic and cathodic reactions.
• Some of the largest scale chemicals are produced via catalytic oxidation, often using
oxygen. Examples include nitric acid (from ammonia), sulfuric acid (from sulfur
dioxide to sulfur trioxide by the chamber process), terephthalic acid from p-xylene,
and acrylonitrile from propane and ammonia.
• Many other chemical products are generated by large-scale reduction, often via
hydrogenation. The largest-scale example is ammonia, which is prepared via the
Haber process from nitrogen. Methanol is prepared from carbon monoxide.
• Bulk polymers derived from ethylene and propylene are often prepared via Ziegler-
Natta catalysis. Polyesters, polyamides, and isocyanates via acid-base catalysis.
• Most carbonylation processes require metal catalysts, examples include the
Monsanto acetic acid process and hydroformylation.
• One of the most obvious applications of catalysis is the hydrogenation (reaction with
hydrogen gas) of fats using nickel catalyst to give margarine. Many other foodstuffs
are prepared via biocatalysis (see below).
• In nature, enzymes are catalysts in metabolism and catabolism. Most biocatalysts
are protein-based, i.e. enzymes,
• Biocatalysts can be thought of as intermediate between homogenous and
heterogeneous catalysts, although strictly speaking soluble enzymes are
homogeneous catalysts and membrane-bound enzymes are heterogeneous. Several
factors affect the activity of enzymes (and other catalysts) including temperature, pH,
concentration of enzyme, substrate, and products. A particularly important reagent in
enzymatic reactions is water, which is the product of many bond-forming reactions
and a reactant in many bond-breaking processes.
• Enzymes are employed to prepare many commodity chemicals including high-
fructose corn syrup and acrylamide.
In the environment
• Catalysis impacts the environment by increasing the efficiency of industrial
processes, but catalysis also directly plays a direct role in the environment. A notable
example is the catalytic role of Chlorine free radicals in the break down of ozone.
These radicals are formed by the action of ultraviolet radiation on
Cl· + O3 → ClO· + O2
ClO· + O· → Cl· + O2
• Cars use this technology to reduce harmful emissions
into the environment.
• NO(g) and NO2(g) emissions are changed to N2 (g) and
• CO(g) emissions are changed to less harmful CO2 (g).
1. #56 – 61 page 34
2. #62-63 page 36