CHM 116 Chapter 15 Lecture Notes Fall 2024 PDF

Upcoming Announcements DUE 09/06 at 11:59 pm MST: CHM 116 ✓ Chapter 14 CC ✓ Chapter 14 HW, Part 1 ✓ Lecture: Chapter 15...

Upcoming Announcements DUE 09/06 at 11:59 pm MST: CHM 116 ✓ Chapter 14 CC ✓ Chapter 14 HW, Part 1 ✓ Lecture: Chapter 15 ✓ Chapter 14 HW, Part 2 ✓ Dr. Chandrakanthan ([email protected]) DUE 09/20 at 11:59 pm MST: In-Person (PSD 304F)/Zoom Office ✓ Chapter 15 CC Hours: ✓ Chapter 15 HW, Part 1 T Th 10:30 am – 11:30 am MST ✓ Chapter 15 HW, Part 2 T Th 1:30 pm – 2:30 pm MST ✓ Course Slack Page: Online Unit 1 Exam is on September https://asu-2247-chm116-70522.slack.com 24th from 6:00 am – 11:59 pm MST in #chm116-homework-course discussions Canvas. Copyright © 2020 Arizona Board of Regents.  CHM 116: Ch 14 Discussion Sessions DS Leaders Discussion sessions via ZOOM Hendrickson Discussion Session Zoom Link: 798 594 5999 Monday 9/2: 10:30 am – 11:30 am No session Sajani Thursday 9/5: 11:15 am – 12:15 pm Ch 14 Part 2 Basnayake (Zoom only) Chandrakanthan Discussion Session Zoom Link: 833 970 7908 Wednesday 9/4: 11:15 am – 12:15 pm Ch 14 Part 3 (Zoom only) Shelly Hauck Thursday 9/5: 1:30 pm – 2:30 pm Q&A Session (In person PSD 222 and Zoom) Copyright © 2020 Arizona Board of Regents. Chemical Equilibrium Chapter 15 Outline What is chemical equilibrium? 15.1 The Concept of Equilibrium How do we quantify equilibrium? 15.2 The Equilibrium Constant 15.3 Using Equilibrium Constants 15.4 Heterogeneous Equilibria 15.5 Calculating Equilibrium Constants 15.6 Reaction Quotient, Q What factors affect equilibrium? 15.7 Le Châtelier’s Principle What is chemical equilibrium? Section 15.1 Why Study Equilibrium?! 𝑵𝟐 𝒈 + 𝟑 𝑯𝟐 𝒈 ⇌ 𝟐 𝑵𝑯𝟑 (𝒈) Consideration of chemical equilibrium is important when trying to maximize production of many chemical compounds. Example: synthesis of ammonia from nitrogen and hydrogen https://www.youtube.com/watch?v=o1_D4FscMnU The Concept of Equilibrium Many chemical reactions do not go to completion. They obtain a state of equilibrium. Equilibrium is a state in which there are no observable changes as time goes by. Physical equilibrium occurs when an equilibrium is achieved between phases. Example: evaporation of bromine 𝑩𝒓𝟐 𝒍 ⇌ 𝑩𝒓𝟐 (𝒈) The Concept of Equilibrium Chemical equilibrium is a state reached by a chemical reaction where: 1. the forward and reverse reactions occur at the same rate. 2. the concentrations of the reactants and the products remain constant. ̶ The concentrations are not necessarily equal. Example: weak acid/base neutralization reactions Remember, weak acids and/or weak bases are WEAK ELECTROLYTES which only partially dissociate. The Concept of Equilibrium 𝑵𝟐 𝑶𝟒 𝒈 ⇌ 𝟐 𝑵𝑶𝟐 (𝒈) Initial: Frozen N2O4 Transition: As N2O4 is warmed above its boiling point, it starts to decompose into NO2 (forward reaction). Equilibrium: The color stops changing when the reactant and the product are interconverting at the same rate. The Concept of Equilibrium Chemical equilibrium is a state Consider the previous reaction: reached by a chemical reaction kf where: N2O4 (g) 2 NO2 (g) 1. The forward and reverse kr reactions occur at the same Rate (forward) = kf[N2O4] rate. Rate (reverse) = kr[NO2]2 2. The concentrations of the reactants and the products At equilibrium: remain constant. ̶ The concentrations are not kf[N2O4] = kr[NO2]2 necessarily equal. The Concept of Equilibrium Consider the previous reaction: kf N2O4 (g) kr 2 NO2 (g) At equilibrium: kf[N2O4] = kr[NO2]2 For many chemical reactions, reactants and products continuously “go back and forth over the activation energy hill.” The Concept of Equilibrium kf N2O4 (g) 2 NO2 (g) kr Equilibrium occurs when the rate of the forward and reverse reactions are the same. The Concept of Equilibrium Chemical equilibrium is a state Consider the previous reaction: reached by a chemical reaction kf where: N2O4 (g) 2 NO2 (g) 1. The forward and reverse kr reactions occur at the same Rate (forward) = kf[N2O4] rate. Rate (reverse) = kr[NO2]2 2. The concentrations of the reactants and the products At equilibrium: remain constant. ̶ The concentrations are not kf[N2O4] = kr[NO2]2 necessarily equal. The Concept of Equilibrium kf N2O4 (g) 2 NO2 (g) kr Equilibrium is established regardless of the initial concentration of reactants/products. Only NO2 Only N2O4 N2O4 + NO2  Concept Check Equilibrium Which of the following statements correctly describes a system at equilibrium? A. The rate constant of the forward reaction is equal with the rate constant of the reverse reaction (kf = kr). B. The concentration of the product(s) are always equal to the concentration of the reactant(s). C. The concentration of the reactants and products will continue changing. D. The rate of the forward reaction is equal to the rate of the reverse reaction. How do we quantify equilibrium? Sections 15.2 – 15.6 The Concept of Equilibrium Equilibrium Constant Expression kf N2O4 (g) 2 NO2 (g) kr Since the total concentrations of reactant and product do not change at equilibrium, the ratio of concentration terms is a constant known as the equilibrium constant (Keq). 𝒌𝒇 𝑵𝑶𝟐 𝟐 = = 𝑲𝒆𝒒 𝒌𝒓 [𝑵𝟐 𝑶𝟒 ] Law of Mass Action The law of mass action, which expresses, for any reaction, the relationship between the concentrations of the reactants and products present at equilibrium. kf For the reaction: aA + bB dD + eE kr the equilibrium condition is described by the expression: [𝑫]𝒅 [𝑬]𝒆 ⟵ products 𝑲𝒄 = [𝑨]𝒂 [𝑩]𝒃 ⟵ reactants  The Equilibrium Constant (Keq) The equilibrium constant (Keq) is a specific ratio of products to reactants that is constant for a reaction at a given temperature. kf For the reaction: aA + bB dD + eE kr General Forms at Equilibrium: [𝑫]𝒅 [𝑬]𝒆 (𝑷𝑫 )𝒅 (𝑷𝑬 )𝒆 𝑲𝒄 = 𝑲𝒑 = [𝑨]𝒂 [𝑩]𝒃 (𝑷𝑨 )𝒂 (𝑷𝑩 )𝒃 Equilibrium concentrations (in molarity). Equilibrium partial pressures (in atm). The brackets indicate molarity Px represents partial pressure. concentration. The Equilibrium Constant (Keq) The equilibrium constant (Keq) is a Kc and Kp are basic designations specific ratio of products to for Keq specific to the way their reactants that is constant for a concentrations were measured. reaction at a given temperature. Can be written directly from the Many names for Keq (sometimes balanced chemical equation. referred to simply as K): Independent of the reaction Ka for acid equilibrium mechanism. Kb for base equilibrium NO UNITS for any type of Kf for formation equilibrium equilibrium constant. Ksp for solubility equilibrium  Concept Check Homogeneous Equilibrium Constant Expression What is the correct equilibrium constant expression (Kc ) for the following reaction? 𝑪𝑶𝟐 𝒈 + 𝟐 𝑯𝟐 𝒈 ⇌ 𝑪𝑯𝟑 𝑶𝑯 𝒈 𝐶𝐻3 𝑂𝐻 A. 𝐶𝑂2 𝐻2 𝐶𝑂2 𝐻2 2 𝑪𝑯𝟑 𝑶𝑯 B. 𝑲𝒄 = 𝐶𝐻3 𝑂𝐻 𝑪𝑶𝟐 [𝑯𝟐 ]𝟐 𝐶𝑂2 𝐻2 C. 𝐶𝐻3 𝑂𝐻 𝐶𝐻3 𝑂𝐻 D. 𝐶𝑂2 𝐻2 2  Concept Check Calculating Equilibrium Constant, Kc What is the equilibrium constant, Kc, for this set of experiments? 𝑵𝟐 𝑶𝟒 𝒈 ⇌ 𝟐 𝑵𝑶𝟐 𝒈 @𝟏𝟎𝟎℃ Initial Initial Equilibrium Equilibrium Exp’t [N2O4] [NO2] [N2O4] [NO2] Kc (M) (M) (M) (M) 1 0.0 0.0200 0.00140 0.0172 2 0.0 0.0300 0.00280 0.0243 3 0.0 0.0400 0.00452 0.0310 4 0.0200 0.0 0.00452 0.0310 The Equilibrium Constant Kc vs. Kp To compare the two forms of the equilibrium constant, consider the reaction: 𝑵𝟐 𝑶𝟒 𝒈 ⇌ 𝟐 𝑵𝑶𝟐 (𝒈) What is Kc? [𝑵𝑶𝟐 ]𝟐 Kp? (𝑷𝑵𝑶𝟐 )𝟐 𝑲𝒄 = 𝑲𝒑 = [𝑵𝟐 𝑶𝟒 ] (𝑷𝑵𝟐 𝑶𝟒 ) In most cases, Kc ≠ Kp so use the following equation to convert between them: 𝑅 = 0.08206 𝐿∙𝑎𝑡𝑚 𝑚𝑜𝑙∙𝐾 𝑲𝒑 = 𝑲𝒄 (𝑹𝑻)∆𝒏 𝑇 = 𝑎𝑏𝑠𝑜𝑙𝑢𝑡𝑒 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑖𝑛 𝐾 ∆𝑛 = 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝒈𝒂𝒔𝒆𝒐𝒖𝒔 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 − Δn applies to RT only 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝒈𝒂𝒔𝒆𝒐𝒖𝒔 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠  Concept Check Converting from Kc to Kp What is the equilibrium constant, Kp, for this set of experiments? 𝑵𝟐 𝑶𝟒 𝒈 ⇌ 𝟐 𝑵𝑶𝟐 𝒈 @𝟏𝟎𝟎℃ Initial Initial Equilibrium Equilibrium Exp’t [N2O4] [NO2] [N2O4] [NO2] Kc (M) (M) (M) (M) 1 0.0 0.0200 0.00140 0.0172  Concept Check Converting from Kc to Kp For the Haber process below, Kc = 9.60 at 300°C. 𝑵𝟐 𝒈 + 𝟑 𝑯𝟐 𝒈 ⇌ 𝟐 𝑵𝑯𝟑 (𝒈) What is the value of Kp for this reaction at this temperature? Understanding and Working with K The Magnitude of K 𝑹𝒆𝒂𝒄𝒕𝒂𝒏𝒕𝒔 ⇌ 𝑷𝒓𝒐𝒅𝒖𝒄𝒕𝒔 The magnitude of Keq gives information about the equilibrium mixture of a reaction: K >> 1 Keq >> 1 (K > 103) Equilibrium will lie to the right and favor products. Keq Q K Q The system proceeds from left to right (toward products) to reach equilibrium. K=Q K=Q The system is already at equilibrium. K