DOCSLIB.ORG

3 Slides Per Page

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
3 Slides Per Page 10/9/2020 64 Lecture #3 of 26 65 Looking forward… our review of Chapter “0” ● Cool applications ● Redox half-reactions ● Balancing electrochemical equations ● History of electrochemistry and Batteries ● IUPAC terminology and Ecell = Ered – Eox ● Thermodynamics and the Nernst equation ● Common reference electrodes ● Standard and Absolute potentials ● Latimer and Pourbaix diagrams ● Calculating Ecell under non-standard state conditions ● Conventions RECALL: Daniell (galvanic) Cell (1836) 66 No more H2 from the (primary) battery! anode cathode oxidation reduction Chemist, Meteorologist Half-reactions are physically separated! 2+ – 2+ – Zn (s) → Zn (aq) + 2e Cu (aq) + 2e → Cu (s) John Frederic Daniell (1790–1845) NET REACTION: Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s) from Wiki 1 10/9/2020 Voltage Produced by Galvanic Cells 67 The difference in electric potential between the anode and the cathode is called: ✓ Cell potential ✓ Cell voltage ✓ emf (electromotive force) This should be –0.76 V! Cell Diagram (we will discuss this soon) Zn (s) + Cu2+ (aq) Cu (s) + Zn2+ (aq) [Cu2+] = 1 M and [Zn2+] = 1 M Zn (s) | Zn2+ (aq, 1 M) || Cu2+ (aq, 1 M) | Cu (s) anode salt bridge cathode EXAMPLE: What is the (standard) potential of a galvanic cell 68 consisting of a Cd electrode in a 1.0 M Cd(NO3)2 solution and a Cr electrode in a 1.0 M Cr(NO3)3 solution? Which half-reaction is reducing? 2+ – 0 Cd (aq) + 2e Cd (s) E = -0.40 V Cd2+ will get reduced to Cd Cr3+ (aq) + 3e– Cr (s) E0 = -0.74 V Cr will get oxidized to Cr3+ More negative of the two … thus, it is reducing Anode (oxidation): Cr (s) Cr3+ (1 M) + 3e– x 2 Cathode (reduction): 2e– + Cd2+ (1 M) Cd (s) x 3 2Cr (s) + 3Cd2+ (1 M) 3Cd (s) + 2Cr3+ (1 M) 0 0 0 Ecell = Ecathode – Eanode 0 Ecell = -0.40 V – (-0.74 V) 0 Ecell = +0.34 V (positive = spontaneous, since ∆퐺 = −푛퐹퐸) … if your answer is negative then you switched the anode/cathode in the galvanic cell Electrochemistry: 69 conventions… oh, conventions! Cathode – electrode where catholyte species are reduced Anode – electrode where anolyte species are oxidized 2 10/9/2020 Electrochemistry: 70 conventions… oh, conventions! Cathode – electrode where catholyte species are reduced Anode – electrode where anolyte species are oxidized Does a Negative/Positive Electrode = Cathode or Anode?… It depends! For the discharging (galvanic) battery, label the anode and the cathode. http://autoshop101.com/ Electrochemistry: 71 conventions… oh, conventions! Cathode – electrode where catholyte species are reduced Anode – electrode where anolyte species are oxidized Does a Negative/Positive Electrode = Cathode or Anode?… It depends! For the charging (electrolytic) battery, label the anode and the cathode. e– e– This is a generator (AKA power supply) cathode anode http://autoshop101.com/ Electrochemistry: 72 conventions… oh, conventions! Positive electrode – positively charged; immersed in the posolyte Negative electrode – negatively charged; immersed in the negolyte … I’m not kidding! … Sheesh!… … Take-home message: For batteries, don’t call electrodes anodes and cathodes (but naming convention used by most is for discharge) e– e– e– e– anode cathode cathode anode http://autoshop101.com/ 3 10/9/2020 Chemist, Meteorologist The Daniell Cell (1836) low impedance to measure current – – Icell John Frederic Daniell (1790–1845) from Wiki As drawn, current flows for < 1 sec and then stops due to Zn Cu lack of charge neutrality… … capacitive charging Zn(s) Zn2+(aq) Cu2+(aq) Cu(s) Zn | Zn2+(aq) || Cu2+(aq) | Cu Chemist, Meteorologist The Daniell Cell (1836) Now it works = “electrochemistry”! low impedance to measure current – – Icell John Frederic Daniell + Ai (1790–1845) from Wiki As drawn, current flows B – i for < 1 sec Salt bridge and then contains an inert, stops due to Zn redox inactive Cu lack of charge salt solution neutrality… (electrolyte) … capacitive charging Zn(s) Zn2+(aq) Cu2+(aq) Cu(s) Zn | Zn2+(aq) || Cu2+(aq) | Cu The Daniell Cell (1836) Quick Quiz * Name the cell type * Identify the anode * Identify the cathode low impedance to measure current * Name the – – electrode signs Icell + * primary galvanic cell Ai … Ultimately, this cell will have fully discharged, and at which point it will B – i be at equilibrium (ΔG = Ecell = 0)… (A/–) (C/+) Zn Cu … Then, any direction of polarization bias will result Zn(s) Zn2+(aq) Cu2+(aq) Cu(s) in electrolytic function (i.e. Zn | Zn2+(aq) || Cu2+(aq) | Cu charging)! 4 10/9/2020 76 Quick Check on Your Understanding You try! (a) What is the standard Ecell for a galvanic cell based on zinc and silver? Ecell = +0.80 V – (-0.76 V) = 1.56 V (b) If one wanted to electrolytically charge the cell from part a (before any reactions took place), what potential would one have to provide? Ebias < –1.56 V… such that Ecell + Ebias < 0 (this is the observed value) 77 International Union of Pure and Applied Chemistry (IUPAC) (Accepted) Nomenclature and Terminology that you’ve learned, but may have forgotten • Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol) differentiate, with respect to time integrate, over time • Electricity is the flow of current (I; in units of A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+) • (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reduction This relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and… … partial molar Gibbs free energy is the electrochemical potential (휇ҧ, in units of J/mol) ➢ Chemical potential (휇, in units of J/mol) ➢ Galvani/Inner (electric) potential (ϕ, in units of V) … and in summary, 휇ҧ = 휇 + 푧퐹ϕ Also, standard state is a solvent, a solid, and a species at unit activity (~1 M solutes, ~1 bar gases) Also, E = IR (Ohm’s law) when resistance is constant • Galvanic cells produce power (in units of W = A x V = C/s x J/C = J/s) by spontaneous redox reactions • Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable • A battery has an anode/anolyte and a cathode/catholyte, but these descriptors change depending on whether the battery is being discharged(Sources (galvanic): B&F, M3LC or charged course (electrolytic); textbook, negative electrode/negolyte and positive electrode/posolyte are better and http://goldbook.iupac.org/) 78 International Union of Pure and Applied Chemistry (IUPAC) (Accepted) Nomenclature and Terminology that you’ve learned, but may have forgotten • Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol) differentiate, with respect to time integrate, over time • Electricity is the flow of current (I; in units of A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+) • (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reduction This relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and… … partial molar Gibbs free energy is the electrochemical potential (휇ҧ, in units of J/mol) Based on➢ourChemicalcurrentpotentialsign convention (휇, in units of J/, molit is) E0(Cu2+/0) = +0.34 V vs. SHE best to ➢onlyGalvani/Innerwrite reduction (electric) potentialpotentials (ϕ, in units; of V) E0(Cu0/2+) = –0.34 V vs. SHE however,… andif inwe summary,lived 휇ҧ =in휇 +an푧퐹ϕ oxidation- Also, standard state is a solvent, a solid, and a species at unit activity (~1 M… solutes, is incorrect! ~1 bar gases) potentialAlso,-centric E = IR (Ohm’sworld, law) whenwe resistancecould iswrite constant them all (i.e. everything) as oxidation You can subtract redox • Galvanic cells produce power (in units of W = A xpotentials V = C/s x J/C but = J/s)do not by spontaneous change the potentialsredox; reactionssimply put, it is best to not sign of the potential and then mix the conventions and so stick with • Electrolytic cells require a power input to drive redoxcall reactions;it an oxidation thus, the potential! reactions are reductionthermodynamicallypotentials unfavorable • A battery has an anode/anolyte and a cathode/catholyte, but these descriptors change depending on whether the battery is being discharged (galvanic) or charged (electrolytic); negative electrode/negolyte and positive electrode/posolyte are better 5 10/9/2020 79 International Union of Pure and Applied Chemistry (IUPAC) (Accepted) Nomenclature and Terminology that you’ve learned, but may have forgotten • Coulomb (in units of C = A·s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant, F ≈ 96,500 C/mol ≈ 105 C/mol) differentiate, with respect to time integrate, over time • Electricity is the flow of current (I; in units of A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e–, H+) • (Electrode) (electric) potential (V or E; in units of V = J/C) is written as a reduction This relates to Gibbs free energy as ΔG = –RT ln K = –nFEcell (electrical work per mole), and… … partial molar Gibbs free energy is the electrochemical potential (휇ҧ, in units of J/mol) ➢ Chemical potential (휇, in units of J/mol) ➢ Galvani/Inner (electric) potential (ϕ, in units of V) Cannot be … and in summary, 휇ҧ = 휇 + 푧퐹ϕ measured Also, standard state is a solvent, a solid, and a species at
Load more

Recommended publications
  • Basic Design Data, of Column for Absorption Of
    j833 Index – a acetyl radical 741 breakthrough curves for H2S adsorption on a absorption 108 acid aerosols 567 molecular sieve 132, 133 – activity and activity coefficients, in acid–base catalyzed reactions 11 – calculation of lads,ideal, HTZ, and LUB chloroform 111 acid catalyst 11 based on breakthrough curves 135 – basic design data, of column for absorption acidity 10 – capillary condensation of CO2 in water 116 acid-catalyzed reaction 652 –– and adsorption/desorption hysteresis 126 – Bunsen absorption coefficient 110 acid-soluble polymers 653 – competitive 128 – – fi chemical absorption of CO2 in N- acrolein 30, 476, 476, 479, 481, 483, 701 design of a xed-bed adsorption process 131 methyldiethanolamine 112, 113 acrylamide 28, 29, 487 – design of processes 130–135 – CO2 in water, and subsequent bicarbonate acrylic acid 140, 466, 467, 479, 481–483 – desorption 131 formation 110 acrylonitrile 462, 466, 467, 486–487 – dissociative 128 – design of columns 113–116 activation energy 24, 34, 201, 203, 215, 711 – equilibrium of a binary system on zeolite 128 – equilibria of chemical absorption 108 – apparent activation energy of diffusion – estimation of slope of breakthrough curve 132 – equilibria of physical absorption, processes 229, 230, 232 – height of mass transfer zone HTZ 132 comparison 109 – for chain transfer 807 – hysteresis loop during – fl – –– gas velocity and ooding of absorption correlation between activation energy and adsorption and desorption of N2 in a column 115 reaction enthalpy for a reversible cylindrical pore 127 – height
    [Show full text]
  • Anal Chem 458.309A Week 5.Pdf
    § Verify this behavior algebraically using the reaction quotient, Q § In one particular equilibrium state of this system, à the following concentrations exist: § Suppose that the equilibrium is disturbed by adding dichromate to the 2- solution to increase the concentration of [Cr2O7 ] from 0.10 to 0.20 M. à In what direction will the reaction proceed to reach equilibrium? § Because Q > K à the reaction must go to the left to decrease the numerator and increase the denominator, until Q = K § If a reaction is at equilibrium and products are added (or reactants are removed), à the reaction goes to the left. § If a reaction is at equilibrium and reactants are added (or products are removed), à the reaction goes to the right § The effect of temperature on K: § The term eΔS°/R is independent of T à ΔS is constant at least over a limited temperature range § If ΔHo is positive, à The term e-ΔH°/RT increases with increasing temperature § If ΔHo is negative, à The term e-ΔH°/RT decreases with increasing temperature § The effect of temperature on K: § If the temperature is raised, à The equilibrium constant of an endothermic reaction (ΔHo>0) increases à The equilibrium constant of an exothermic reaction (Δho<0) decreases § If the temperature is raised, à an endothermic reaction is favored § If the temperature is raised, then heat is added to the system. à The reaction proceeds to partially offset this heat à an endothermic reaction à Le Châtelier’s principle Solubility product § The equilibrium constant for the reaction in which a solid salt dissolves to give its constituent ions in solution.
    [Show full text]
  • Main Criteria: AP Chemistry Course Description Secondary Criteria: Jove Subject: Science Grade: 9-12 Correlation Options: Show Correlated Adopted: 2013
    Main Criteria: AP Chemistry Course Description Secondary Criteria: JoVE Subject: Science Grade: 9-12 Correlation Options: Show Correlated Adopted: 2013 Outline Level 1 AP.C.1. Big Idea 1: The chemical elements are fundamental building materials of matter, and all matter can be understood in terms of arrangements of atoms. These atoms retain their identity in chemical reactions. Outline Level 2 EU.1.A. All matter is made of atoms. There are a limited number of types of atoms; these are the elements. Outline Level 3 EK.1.A.1. Molecules are composed of specific combinations of atoms; different molecules are composed of combinations of different elements and of combinations of the same elements in differing amounts and proportions. Outline Level 4 1.A.1.a. The average mass of any large number of atoms of a given element is always the same for a given element. JoVE • Freezing-Point Depression to Determine an Unknown Compound • Introduction to Mass Spectrometry • MALDI-TOF Mass Spectrometry • Tandem Mass Spectrometry Outline Level 4 1.A.1.b. A pure sample contains particles (or units) of one specific atom or molecule; a mixture contains particles (or units) of more than one specific atom or molecule. JoVE • Calibration Curves • Capillary Electrophoresis (CE) • Chromatography-Based Biomolecule Purification Methods • Column Chromatography • Conducting Reactions Below Room Temperature • Cyclic Voltammetry (CV) • Degassing Liquids with Freeze-Pump-Thaw Cycling • Density Gradient Ultracentrifugation • Determining the Density of a Solid and Liquid
    [Show full text]
  • Unit IV Outiline
    CHEMISTRY 111 LECTURE EXAM IV Material PART 1 CHEMICAL EQUILIBRIUM Chapter 14 I Dynamic Equilibrium I. In a closed system a liquid obtains a dynamic equilibrium with its vapor state Dynamic equilibrium: rate of evaporation = rate of condensation II. In a closed system a solid obtains a dynamic equilibrium with its dissolved state Dynamic equilibrium: rate of dissolving = rate of crystallization II Chemical Equilibrium I. EQUILIBRIUM A. BACKGROUND Consider the following reversible reaction: a A + b B ⇌ c C + d D 1. The forward reaction (⇀) and reverse (↽) reactions are occurring simultaneously. 2. The rate for the forward reaction is equal to the rate of the reverse reaction and a dynamic equilibrium is achieved. 3. The ratio of the concentrations of the products to reactants is constant. B. THE EQUILIBRIUM CONSTANT - Types of K's Solutions Kc Gases Kc & Kp Acids Ka Bases Kb Solubility Ksp Ionization of water Kw Hydrolysis Kh Complex ions βη Page 1 General Keq Page 2 C. EQUILIBRIUM CONSTANT For the reaction, aA + bB ⇌ cC + dD The equilibrium constant ,K, has the form: [C]c [D]d Kc = [A]a [B]b D. WRITING K’s 1. N2(g) + 3 H2(g) ⇌ 2 NH3(g) 2. 2 NH3(g) ⇌ N2(g) + 3 H2(g) E. MEANING OF K 1. If K > 1, equilibrium favors the products 2. If K < 1, equilibrium favors the reactants 3. If K = 1, neither is favored F. ACHIEVEMENT OF EQUILIBRIUM Chemical equilibrium is established when the rates of the forward and reverse reactions are equal. CO(g) + 3 H2(g) ⇌ CH4 + H2O(g) Initial amounts moles H 2 Equilibrium amounts moles CO moles CH = moles water 4 Time Page 3 G.
    [Show full text]
  • Theoretical Problem Icho 2019
    Candidate: AAA-1 THEORETICAL EXAM Making science together! 2019-07-26 51st IChO – Theoretical Exam 1 Candidate: AAA-1 General instructions This theoretical exam booklet contains 60 pages. You may begin writing as soon as the Start command is given. You have 5 hours to complete the exam. All results and answers must be clearly written in pen in their respective designed areas on the exam papers. Answers written outside the answer boxes will not be graded. If you need scratch paper, use the backside of the exam sheets. Remember that nothing outside the designed areas will be graded. Use only the pen and calculator provided. The official English version of the exam booklet is available upon request and serves for clarification only. If you need to leave the exam room (to use the toilet or have a snack), wave the corresponding IChO card. An exam supervisor will come to accompany you. For multiple-choice questions: if you want to change your answer, fill the answer box completely and then make a new empty answer box next to it. The supervisor will announce a 30-minute warning before the Stop command. You must stop your work immediately when the Stop command is announced. Failure to stop writing by ½ minute or longer will lead to nullification of your theoretical exam. After the Stop command has been given, place your exam booklet back in your exam envelope, then wait at your seat. The exam supervisor will come to seal the envelope in front of you and collect it. GOOD LUCK! 51st IChO – Theoretical Exam 2 Candidate: AAA-1 Table of Contents This theoretical exam is composed of 9 independent problems, as follows.
    [Show full text]
  • Lithium Batteries
    Batteries General planning of the „Lithium Batteries” lab for the European Master 2007/8 Warsaw University of Technology, Departament of Inorganic Chemistry and Solid State Technology, Dr Marek Marcinek Objectives: Students will: follow the development of primary and secondary lithium batteries become familiar with different types of batteries explore the applications of batteries study the major components of lithium (ion) cells learn which batteries can be recycled realize the economic and environmental advantages of using rechargeable batteries Needs: Room with avialiables 2 desks and 2 computers or Multimedia Projector Potentiostat/galvanostat with galvanic cycle mode. Suplementary materials needed for: Building the simple battery (included Volta cell) Daniell cell Leclanche Cell Commercially available variety of Li-bat (also disassembled in a controlled mode) BDS software Safety issues: Safety rules Read directions carefully before you begin any experiments. Clear an area to work. Wash your hands thoroughly after experimenting Do always wear eye protection Keep all chemicals away from your eyes and mouth Do not eat and drink in your experiment area Put all pieces of equipment away when finished using them General First aid information Indicate the person who should IMMIDIATELLY inform the teacher and ask the other person to help you out if needed. Eyes: rinse immediately with water. Remove contact lenses if wearing any. Flush eyes with water for 15 min Swallowed: Rinse mouth Drink glass full of water or milk. DO NOT INDUCE VOMITING SKIN: Flush skin thoroughly with water. In all cases, get immediate medical attention if an emergency exists. Bring the chemical container with you. 1 Materials given to students/preparation: Exemplary 5 scientific papers (or any material found related to the Battery Performance, Design, Safety, Application) for individual preparation.
    [Show full text]
  • The Metallic World
    UNIT 11 The Metallic World Unit Overview This unit provides an overview of both electrochemistry and basic transition metal chemistry. Oxidation-reduction reactions, also known as redox reactions, drive electrochemistry. In redox reactions, one compound gains electrons (reduction) while another one loses electrons (oxidation). The spontaneous directions of redox reactions can generate electrical current. The relative reactivities of substances toward oxidation or reduction can promote or prevent processes from happening. In addition, redox reactions can be forced to run in their non-spontaneous direction in order to purify a sample, re-set a system, such as in a rechargeable battery, or deposit a coating of another substance on a surface. The unit also explores transition metal chemistry, both in comparison to principles of main-group chemistry (e.g., the octet rule) and through various examples of inorganic and bioinorganic compounds. Learning Objectives and Applicable Standards Participants will be able to: 1. Describe the difference between spontaneous and nonspontaneous redox processes in terms of both cell EMF (electromotive force) and DG. 2. Recognize everyday applications of spontaneous redox processes as well as applications that depend on the forcing of a process to run in the non-spontaneous direction. 3. Understand the basics of physiological redox processes, and recognize some of the en- zymes that facilitate electron transfer. 4. Compare basic transition-metal chemistry to main-group chemistry in terms of how ions are formed and the different types of bonding in metal complexes. Key Concepts and People 1. Redox Reactions: Redox reactions can be analyzed systematically for how many electrons are transferred, whether or not the reaction happens spontaneously, and how much energy can be transferred or is required in the process.
    [Show full text]
  • Sequencing Instruction in Chemistry: Simulation Or Traditional First?
    SEQUENCING INSTRUCTION IN CHEMISTRY: SIMULATION OR TRADITIONAL FIRST? by Sharmila Pillay B.Sc., The University of South Pacific, 1994 B.Ed., The University of British Columbia, 1999 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in THE FACULTY OF GRADUATE STUDIES (Science Education) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) October 2010 ©Sharmila Pillay, 2010 ABSTRACT The purpose of this study is to investigate how a technology-enhanced lesson based on the principles of model-based teaching and learning can contribute to student understanding of two challenging topics in chemistry: Le Chatelier’s Principle and Chemical Equilibrium. A computer simulation program was utilized that contained multiple digital representations, such as: a chemical formula view, a slider view, a graph view, a description view, a prediction view, a molecular view and a dynamic analogy view. The study also addressed the sequencing of instruction, changing when computer simulation was introduced in two chemistry 12 classes (n=46). One class of 22 students received instruction in a traditional form (lecture, labs) and then interacted with the simulation and the other class of 24 students interacted with simulations first and then received a traditional form of instruction. Both the classes participated in a pre-test, mid-test, post-test, surveys and interviews designed to assess students’ conceptual understanding of chemical equilibrium. Statistical analysis of the tests revealed that a computer simulation such as Technology-Enhanced Model-Based Science (TEMBS) promoted understanding by supporting the generation of more scientifically accurate models of chemical equilibrium. Secondly, there was a significant improvement in test results of students who received instruction in a traditional form first and then interacted with simulations compared with students who interacted with simulations first and then received traditional instruction.
    [Show full text]
  • Battery Technologies for Small Scale Embeded Generation
    Battery Technologies for Small Scale Embedded Generation. by Norman Jackson, South African Energy Storage Association (SAESA) Content Provider – Wikipedia et al Small Scale Embedded Generation - SSEG • SSEG is very much a local South African term for Distributed Generation under 10 Mega Watt. Internationally they refer to: Distributed generation, also distributed energy, on-site generation (OSG) or district/decentralized energy It is electrical generation and storage performed by a variety of small, grid- connected devices referred to as distributed energy resources (DER) Types of Energy storage: • Fossil fuel storage • Thermal • Electrochemical • Mechanical • Brick storage heater • Compressed air energy storage • Cryogenic energy storage (Battery Energy • Fireless locomotive • Liquid nitrogen engine Storage System, • Flywheel energy storage • Eutectic system BESS) • Gravitational potential energy • Ice storage air conditioning • Hydraulic accumulator • Molten salt storage • Flow battery • Pumped-storage • Phase-change material • Rechargeable hydroelectricity • Seasonal thermal energy battery • Electrical, electromagnetic storage • Capacitor • Solar pond • UltraBattery • Supercapacitor • Steam accumulator • Superconducting magnetic • Thermal energy energy storage (SMES, also storage (general) superconducting storage coil) • Chemical • Biological • Biofuels • Glycogen • Hydrated salts • Starch • Hydrogen storage • Hydrogen peroxide • Power to gas • Vanadium pentoxide History of the battery This was a stack of copper and zinc Italian plates,
    [Show full text]
  • The Equilibrium Constant
    Chapter 15: Chemical Equilibrium Key topics: Equilibrium Constant Calculating Equilibrium Concentrations The Concept of Equilibrium Consider the reaction k1 A ⌦ B k 1 − At equilibrium there is no net change in [A] or [B], namely d[A] d[B] =0= dt dt But A molecules can react to form B, and B molecules can react to form A, if the forwards and backwards rates are equal. k1[A] = k 1[B] − This is because d[A] = k1[A] + k 1[B] dt − − At the molecular level, typically the reactions do not stop. Initially there is net evaporation of liquid, but after dynamic equilibrium is established, the rate of evaporation = rate of condensation. (from chemtutorial.net) Consider the reaction N2O4(g) 2NO2(g) Begin with only N2O4 (colorless). Begin with only NO2 (brown). 2 The forward rate = kf [N2O4]; the reverse rate = kr [NO2] (the elementary reactions are the same as the overall reaction) In both cases equilibrium is established after some time. The Equilibrium Constant At equilibrium the forwards and reverse rates are equal 2 2 kf [NO2]eq kf [N2O4]eq = kr[NO2]eq = = Kc ) kr [N2O4]eq Kc is the equilibrium constant (the “c” here stands for concentration). In general, to write an equilibrium constant o products over reactants o exponents are the coefficients from the balanced reaction Magnitude of the Equilibrium Constant o If Kc >> 1, products are favored (rxn nearly complete). o If Kc << 1, reactants are favored (rxn hardly proceeds). o If Kc is close to 1, the system contains comparable amounts of products and reactants.
    [Show full text]
  • Chapter 14. CHEMICAL EQUILIBRIUM
    Chapter 14. CHEMICAL EQUILIBRIUM 14.1 THE CONCEPT OF EQUILIBRIUM AND THE EQUILIBRIUM CONSTANT Many chemical reactions do not go to completion but instead attain a state of chemical equilibrium. Chemical equilibrium: A state in which the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constant. ⇒ Equilibrium is a dynamic process – the conversions of reactants to products and products to reactants are still going on, although there is no net change in the number of reactant and product molecules. For the reaction: N2O4(g) 2NO2(g) N 2O4 Forward rate concentration NO Rate 2 Reverse rate time time The Equilibrium Constant For a reaction: aA + bB cC + dD [C]c [D]d equilibrium constant: Kc = [A]a [B]b The equilibrium constant, Kc, is the ratio of the equilibrium concentrations of products over the equilibrium concentrations of reactants each raised to the power of their stoichiometric coefficients. Example. Write the equilibrium constant, Kc, for N2O4(g) 2NO2(g) Law of mass action - The value of the equilibrium constant expression, Kc, is constant for a given reaction at equilibrium and at a constant temperature. ⇒ The equilibrium concentrations of reactants and products may vary, but the value for Kc remains the same. Other Characteristics of Kc 1) Equilibrium can be approached from either direction. 2) Kc does not depend on the initial concentrations of reactants and products. 3) Kc does depend on temperature. Magnitude of Kc ⇒ If the Kc value is large (Kc >> 1), the equilibrium lies to the right and the reaction mixture contains mostly products.
    [Show full text]
  • A Virtual Experiment for Learning the Principle of Daniell Cell Based on Augmented Reality
    applied sciences Article A Virtual Experiment for Learning the Principle of Daniell Cell Based on Augmented Reality Wernhuar Tarng , Yu-Jun Lin and Kuo-Liang Ou * Institute of Learning Sciences and Technologies, National Tsing Hua University, Hsinchu 30013, Taiwan; [email protected] (W.T.); [email protected] (Y.-J.L.) * Correspondence: [email protected]; Tel.: +88-(63)-571-5131 Abstract: Chemistry is a science emphasizing both theory and experimentation. After learning the theoretical knowledge, experimental operation can help students understand chemical concepts and transform them into practical knowledge. Considering the safety issue and the lack of teaching time and experimental equipment, some teachers often choose to demonstrate an experiment instead of letting students conduct it by themselves. This may affect their learning motivation as well as the construction of chemical concepts and hands-on skills. This study combined the augmented reality (AR) technology with the operating principle of the Daniell cell to develop a virtual experiment for the application in high school chemistry courses. Students can conduct the virtual experiment using mobile devices by selecting the required equipment and materials from a deck of cards to set up the experimental environment. In the virtual experiment, students can use the galvanometer to measure the current after mounting the salt bridge on the beakers containing zinc sulfate and copper sulfate solutions. They can also see the change of molecular structures and movement of electrons and ions during the redox reactions to understand the important concepts and knowledge. An empirical research has been performed, and the analytical results show that both the virtual experiment and the real experiment could improve students’ learning achievement, but the former was more effective for the low-achievement students because they could explore autonomously to enhance cognition by observing the submicroscopic view of the redox reactions.
    [Show full text]