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Chapter 14 – Fundamentals of Electrochemistry

Chapter 14 – Fundamentals of Electrochemistry. Homework - Due Friday, April 1 Problems: 14-4, 14-5, 14-8, 14-12, 14-15, 14-17, 14-18, 14-25, 14-26, 14-41, . Electrochemistry Review of the Basics. Oxidation Loss of electrons Always occurs at the anode

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Chapter 14 – Fundamentals of Electrochemistry

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  1. Chapter 14 – Fundamentals of Electrochemistry Homework - Due Friday, April 1 Problems: 14-4, 14-5, 14-8, 14-12, 14-15, 14-17, 14-18, 14-25, 14-26, 14-41, CHM 320 - Lecture 23 Chapt 14

  2. Electrochemistry Review of the Basics • Oxidation • Loss of electrons • Always occurs at the anode • Happens because of the action of a reducing agent • Reduction • Gain of electrons (charge is reduced) • Always occurs at the cathode • Happens because of the action of the oxidizing agent Fe+3 + e- = Fe+2 CHM 320 - Lecture 23 Chapt 14

  3. Redox Reaction ox1 + red2 = red1 + ox2 Example: 2(e- + Fe+3 = Fe+2) + Sn+2 = Sn+4 + 2 e- ------------------------------------------- 2 Fe+3 + Sn+2 = 2 Fe+2 + Sn+4 So… ox1= Fe+3 , red2 = Sn+2, red1=Fe+2, ox2=Sn+4 CHM 320 - Lecture 23 Chapt 14

  4. 4 Electric Charge (in Coulombs) and Work • Voltage represents electrical potential (potential to do work) • If some total charge in coulombs (q) is moved through some electrical potential (E, in volts V) then work is done! • The charge in coulombs (q) is equal to the number of moles of electrons (n) times the Faraday Constant (F) CHM 320 - Lecture 23 Chapt 14

  5. Ohm’s Law and Power • Ohm’s law relates electrical resistance, current and potential! • Power is the work done in some unit time (e.g. joules of work per second) • The units of Power are Watts (W) • Ohm’s law and power are related! CHM 320 - Lecture 23 Chapt 14

  6. Let’s Work Some Problems • A 6.00V battery is connected across a 2.00 K resistor, how many electrons flow through the circuit per second? • How many joules of heat (heat is work) are produced per electron? • What voltage would the battery need to be to deliver a power at 100.0 Watts? CHM 320 - Lecture 23 Chapt 14

  7. Electrochemical Cells • There are two basic electrochemical cells: • A GALVANIC cell uses spontaneous chemical reactions to generate electricity • A ELECTROYLTIC cell requires an electrical potential to be applied to the cell to drive some reaction. • A complete cell contains: • anode • cathode • completed circuit (for electrons to flow) • a salt bridge (usually!) • an electrolyte solution • chemical species that undergo reaction. CHM 320 - Lecture 23 Chapt 14

  8. Galvanic Cell Cells and Cell Reactions Overall Cell Reaction Zn(s) + Cu+2(aq) ---> Zn+2(aq) + Cu(s) oxidation half reaction anode Zn(s) ---> Zn+2(aq) + 2 e- reduction half reaction cathode Cu+2(aq) + 2 e- ---> Cu(s) CHM 320 - Lecture 23 Chapt 14

  9. CHM 320 - Lecture 23 Chapt 14

  10. CHM 320 - Lecture 23 Chapt 14

  11. What is happening at the electrode(s) and how do we describe the cell? CHM 320 - Lecture 23 Chapt 14

  12. The Standard Hydrogen Electrode (SHE) • The basis by which all other measurements are made. • Assigned a potential of zero by definition! • Not practical for regular use Hydrogen Half-Cell H2(g) = 2 H+(aq) + 2 e- reversible reaction SHE consists of a platinum electrode covered with a fine powder of platinum around which H2(g) is bubbled. Its potential is defined as zero volts. CHM 320 - Lecture 23 Chapt 14

  13. CHM 320 - Lecture 23 Chapt 14

  14. CHM 320 - Lecture 23 Chapt 14

  15. Standard Potentials • Standardized potentials (Eo), listed as reductions, for all half-reactions • Measured versus the S.H.E (0) • Used in predicting the action in either a galvanic cell or how much energy would be needed to force a specific reaction in a non-spontaneous cell • Assumes an activity of one for the species of interest (usually a fair approximation) at a known temperature in a cell with the S.H.E. • Assumes that the cell of interest is connected to the (+) terminal of the potentiometer (voltmeter) and the S.H.E. is connected to the (-) terminal CHM 320 - Lecture 23 Chapt 14

  16. Better Oxidizing Agents in upper left hand corner. Better Reducing Agents in lower Right hand corner CHM 320 - Lecture 23 Chapt 14

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