1. Reaction Kinetics Chapter 17 Modern Chemistry
Sections 1 & 2
The Reaction Process
Reaction Rate
Chapter 17 Section 1 The Reaction Process p

2. Chapter 17 Section 1 The Reaction Process p. 560-567

3. Chapter 17 Section 1 The Reaction Process p. 560-567
Reaction Mechanisms
H2 (g) + I2 (g)  2HI (g)
This balanced equations doesn’t show the steps of this reaction.
The step-by-step sequence of reactions by which the overall chemical change occurs is a Reaction Mechanism.
Chapter 17 Section 1 The Reaction Process p

4. Chapter 17 Section 1 The Reaction Process p. 560-567
Reaction Mechanisms
H2 (g) + I2 (g)  2HI (g)
Only the net chemical change is directly observable for most chemical reactions.
Even a reaction that appears from its balanced equation to be a simple process may actually be the result of several simple steps
Chapter 17 Section 1 The Reaction Process p

5. Chapter 17 Section 1 The Reaction Process p. 560-567
Reaction Mechanisms
H2 (g) + I2 (g)  2HI (g)
Step 1: I2 ↔ 2I
Step 2: 2I + H2 ↔ 2HI
I2 + H2 ↔ 2HI
2I is not in the final equation
Chapter 17 Section 1 The Reaction Process p

6. Chapter 17 Section 1 The Reaction Process p. 560-567
Reaction Mechanisms
H2 (g) + I2 (g)  2HI (g)
Step 1: I2 ↔ 2I
Step 2: 2I + H2 ↔ 2HI
I2 + H2 ↔ 2HI
Species that appear in some steps but not in the net equation are known as intermediates.
Chapter 17 Section 1 The Reaction Process p

7. Chapter 17 Section 1 The Reaction Process p. 560-567
Reaction Mechanisms
H2 (g) + I2 (g)  2HI (g)
Step 1: I2 2I
Step 2: I + H2 ↔H2I
Step 3: H2I + I ↔2HI
I2 + H2 ↔2HI
Homogeneous reaction, a reaction whose reactants and products exist in a single phase.
Chapter 17 Section 1 The Reaction Process p

8. Chapter 17 Section 1 The Reaction Process p. 560-567
Reaction Mechanisms
H2 (g) + I2 (g)  2HI (g)
Step 1: I2 2I
Step 2: I + H2 ↔H2I
Step 3: H2I + I ↔2HI
I2 + H2 ↔2HI
Chapter 17 Section 1 The Reaction Process p

9. Chapter 17 Section 1 The Reaction Process p. 560-567
Reaction Mechanism
Chapter 17 Section 1 The Reaction Process p

10. Chapter 17 Section 1 The Reaction Process p. 560-567
Rate Determining Step
Chapter 17 Section 1 The Reaction Process p

11. Chapter 17 Section 1 The Reaction Process p. 560-567
Collision Theory
In order for reactions to occur between substances, their particles must collide.
The particles must collide with the CORRECT ORIENTATION and with SUFFICIENT ENERGY to break the bonds.
Chapter 17 Section 1 The Reaction Process p

12. Chapter 17 Section 1 The Reaction Process p. 560-567
3 Possible Collisions
Chapter 17 Section 1 The Reaction Process p
p. 563

13. Chapter 17 Section 1 The Reaction Process p. 560-567
HI Collisions
Chapter 17 Section 1 The Reaction Process p

14. Chapter 17 Section 1 The Reaction Process p. 560-567
Activation Energy
Chapter 17 Section 1 The Reaction Process p

15. Chapter 17 Section 1 The Reaction Process p. 560-567
Activation Energy
The bonds of these reactants must be broken in order for new bonds to be formed.
Bond BREAKING is an ENDOTHERMIC process, and bond FORMING is EXOTHERMIC.
Activation energy, Ea, is the minimum energy required to transform the reactants into an activated complex.
Chapter 17 Section 1 The Reaction Process p

16. Chapter 17 Section 1 The Reaction Process p. 560-567
Activated Complex
An activated complex is a transitional structure that results from an effective collision and that persists while old bonds are breaking and new bonds are forming .
An activated complex occurs at a high energy position along the reaction pathway.
An activated complex is not the same as an intermediate. – An activated complex is short-lived
Chapter 17 Section 1 The Reaction Process p

17. Chapter 17 Section 1 The Reaction Process p. 560-567
Ch 17 Sec 1 Homework
Page 567 # 1-8
Chapter 17 Section 1 The Reaction Process p

18. Chapter 17 Section 1 The Reaction Process p. 560-567
Energy Profile E
Chapter 17 Section 1 The Reaction Process p
p. 564

19. Chapter 17 Section 1 The Reaction Process p. 560-567
Energy Profiles
Ea = energy of activated complex − energy of reactants [reactants to A.C. on graph]
Ea′ = energy of activated complex − energy of products [products to A.C. on graph]
ΔEforward = energy of products − energy of reactants [reactants to products on graph]
ΔEreverse = energy of reactants − energy of products [products to reactants on graph] |Eforward | = |Ereverse | same value; opposite sign
Chapter 17 Section 1 The Reaction Process p

20. Endothermic Energy Profile
Chapter 17 Section 1 The Reaction Process p

21. Exothermic Energy Profile
Chapter 17 Section 1 The Reaction Process p

22. Energy Profile for HI Synthesis
notes
Energy Profile for HI Synthesis
Chapter 17 Section 1 The Reaction Process p
p. 565

23. Chapter 17 Section 1 The Reaction Process p. 560-567
Sample Problems p. 566
Copy the energy diagram below, and label the reactants, products, E, Ea, and Ea′. Determine the value of Eforward , Ereverse , Ea, and Ea′.
Chapter 17 Section 1 The Reaction Process p

24. Chapter 17 Section 1 The Reaction Process p. 560-567
Sample Problems p. 566
ΔEforward = energy of products − energy of reactants
ΔEforward = 50 kJ/mol − 0 kJ/mol = +50 kJ/mol
ΔEreverse = energy of reactants − energy of products
ΔEreverse = 0 kJ/mol − 50 kJ/mol = − 50 kJ/mol
Chapter 17 Section 1 The Reaction Process p

25. Chapter 17 Section 1 The Reaction Process p. 560-567
Sample Problems p. 566
Ea = energy of activated complex − energy of reactants
Ea = 80 kJ/mol − 0 kJ/mol = 80 kJ/mol
Ea′ = energy of activated complex − energy of products
Ea′ = 80 kJ/mol − 50 kJ/mol = 30 kJ/mol
Chapter 17 Section 1 The Reaction Process p

26. Chapter 17 Section 1 The Reaction Process p. 560-567
Practic Problems p. 567
1. a. Use the method shown in the sample problem to redraw and label the following energy diagram. Determine the value of ΔEforward, ΔEreverse, Ea, and Ea′.
b. Is the forward reaction shown in the diagram exothermic or endothermic? Explain your answer.
Chapter 17 Section 1 The Reaction Process p

27. Chapter 17 Section 1 The Reaction Process p. 560-567
Practic Problems p. 567
2. a. Draw and label an energy diagram similar to the one shown in the sample problem for a reaction in which Ea = 125 kJ/mol and Ea′ = 86 kJ/mol. Place the reactants at energy level zero.
b. Calculate the values of ΔEforward and ΔEreverse.
c. Is this reaction endothermic or exothermic? Explain your answer.
Chapter 17 Section 1 The Reaction Process p

28. Chapter 17 Section 1 The Reaction Process p. 560-567
Practic Problems p. 567
3. a. Draw and label an energy diagram for a reaction in which Ea = 154 kJ/mol and ΔE = 136 kJ/mol.
b. Calculate the activation energy, Ea′, for the reverse reaction.
Chapter 17 Section 1 The Reaction Process p

29. Chapter 17 Section 1 The Reaction Process p. 560-567
Ch 17 Sec 1 Homework
Energy Diagram Worksheet
Chapter 17 Section 1 The Reaction Process p