Reaction Kinetics Chapter 17 Modern Chemistry Sections 1 & 2 The Reaction Process Reaction Rate Chapter 17 Section 1 The Reaction Process p. 560-567

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

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. 560-567

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. 560-567

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. 560-567

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. 560-567

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. 560-567

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. 560-567

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

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

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. 560-567

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

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

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

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. 560-567

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. 560-567

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. 560-567

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

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. 560-567

Endothermic Energy Profile Chapter 17 Section 1 The Reaction Process p. 560-567

Exothermic Energy Profile Chapter 17 Section 1 The Reaction Process p. 560-567

Energy Profile for HI Synthesis notes Energy Profile for HI Synthesis Chapter 17 Section 1 The Reaction Process p. 560-567 p. 565

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. 560-567

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. 560-567

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. 560-567

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. 560-567

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. 560-567

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. 560-567

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. 560-567