To accompany Inquiry into
Chemistry
PowerPoint Presentation
prepared by Robert Schultz
robert.schultz@ei.educ.ab.ca
Chemistry 30 – Unit 1C Activation
Energy and Catalysts
Section 11.1 Reaction Pathways
Chapter 11, Section 11.1
• Reaction rate
• Theory: Collision Theory
• To be an effective collision, need:
• Correct collision geometry
• Sufficient collision energy
Chapter 11, Section 11.1
• Correct collision geometry
• Textbook illustration for
• NO(g) + NO3(g)
2 NO2(g)
Chapter 11, Section 11.1
• Activation energy, Ea – the minimum
collision energy required for a
successful reaction (given that collision
geometry is correct)
• As temperature increases (recall:
temperature is a measure of average Ek
of the particles) more particles have
sufficient energy
• See figure 11.4 page 405
Chapter 11, Section 11.1
• As a result at a higher temperature,
reactions tend to be faster
Chapter 11, Section 11.1
• Recall Ep diagrams, Chapter 9
• More complete Ep diagrams:
Chapter 11, Section 11.1
• In general, reactions with low
activation energies tend to be faster
than reactions with higher activation
energies
• It is impossible to predict reaction
rates (or whether or not a reaction is
spontaneous) from enthalpy changes
Chapter 11, Section 11.1
• Note that forward and reverse activation
energies are both shown on the graphs
• Your book gives the following relationships:
Exothermic: Ea (rev )  Ea ( fwd )  H
Endothermic: Ea (rev )  Ea ( fwd )  H
Book has  r H ; this is a mistake
Rather than memorize these I would
encourage you to merely look at the
graphs:
Chapter 11, Section 11.1
• To get Ea (fwd), measure difference from
reactants to transition state
• To get Ea (rev), measure difference from
products to transition state
Ea (rev)
Ea (fwd)
Ea (fwd)
∆H
∆H
Can you justify the relationships on the previous
page?
Ea (rev)
Chapter 11, Section 11.1
• The chemical species that exists at the
transition state in an Ep diagram is
called the “activated complex”
• Figure 11.8, page 408 in your text,
shows an Ep diagram with a “reaction
snapshot sequence”
• This is theoretical, these are not actual
photos
Chapter 11, Section 11.1
Chapter 11, Section 11.1
• Try Practice Problems 2 and 4 page 409
Chapter 11, Section 11.1
• Do 11.1 Review, page 410,
• questions 1, 2, 5, 6 (hint: draw a rough
diagram), 8
Chapter 11, Section 11.2
• Catalyst: a substance that increases the
rate of a chemical reaction without
being consumed by the reaction
• Considering what you have learned
about reaction rates can you think of
how a catalyst might accomplish this?
• Catalysts provide an alternate reaction
pathway with a lower activation energy
figure 11.10, page 412
Chapter 11, Section 11.2
Review question 4 at top of page 413
Chapter 11, Section 11.2
• Question 4
lowers
• a) A catalyst
• b) A catalyst lowers
• c) A catalyst has no effect
increases
• d) A catalyst
of the forward reaction
increases
• e) A catalyst
of the reverse reaction
Ea (fwd)
Ea (rev)
on ΔH
the speed
the speed
Chapter 11, Section 11.2
• Note the series of 4 photographs in
figure 11.11 on page 413
Chapter 11, Section 11.2
• Read pages 413 to 414 about catalysts
in industry and catalysts in car exhaust
systems
• Discuss
• Read about enzymes, pages 415 to 416
• Do 11.2 Review, page 418, questions
1-6
Chapter 11, Section 11.2