ELECTROCHEMISTRY Presentation by: P.K. CHOURASIA K.V MANDLA, Jabalpur Region

OBJECTIVES Electrochemistry is the study of production of electricity from the energy released during a spontaneous reaction and use of electrical energy to bring about non spontaneous chemical reaction. How Commercially generate electricity. It provides many ideas for protection of metal surface from corrosion.

Chapter 18Slide 3 Redox reaction are those involving the oxidation and reduction of species. OIL – Oxidation Is Loss of electrons. RIG – Reduction Is Gain of electrons. Oxidation and reduction must occur together. They cannot exist alone. Redox Reactions

Chapter 18Slide 4 Redox Reactions Reduction Half-Reaction: Cu 2+ (aq) + 2 e –  Cu(s) The Cu 2+ gains two electrons to form copper.

Chapter 18Slide 5 Oxidation Half-Reaction: Zn(s)  Zn 2+ (aq) + 2 e –. The Zn loses two electrons to form Zn 2+. Redox Reactions

Chapter 18Slide 6 Electrochemical Cells Electrodes: are usually metal strips/wires connected by an electrically conducting wire. Salt Bridge: is a U-shaped tube that contains a gel permeated with a solution of an inert electrolyte. Anode: is the electrode where oxidation takes place. Cathode: is the electrode where reduction takes place.

Chapter 18Slide 7 Electrochemical Cells Convention for expressing the cell: – Anode Half-Cell || Cathode Half-Cell – Electrode | Anode Soln || Cathode Soln | Electrode – Zn(s) | Zn 2+ (1 M) || Cu 2+ (1 M) | Cu(s) Electrons flow from anode to cathode. Anode is placed on left by convention.

Chapter 18Slide 8 Electrochemical Cells Overall: Zn(s) + Cu 2+ (aq)  Zn 2+ (aq) + Cu(s) Left Electrode Right Electrode

Chapter 18Slide 9 Electrochemical Cells Electrode potential: The tendecy of an element when it is placed in contact with its ions, to become positively or negatively charged by losing and gaining electrons. The standard potential of any galvanic cell is the subtraction of the standard half-cell potentials for the oxidation and reduction half-cells. E° cell = E° reduction - E° oxidation Standard half-cell potentials are always quoted as a reduction process. The sign must be changed for the oxidation process.

Chapter 18Slide 10 Electrochemical Cells The standard half-cell potentials are determined from the difference between two electrodes. The reference point is called the standard hydrogen electrode (S.H.E.) and consists of a platinum electrode in contact with H 2 gas (1 atm) and aqueous H + ions (1 M). The standard hydrogen electrode is assigned an arbitrary value of exactly 0.00 V.

Chapter 18Slide 11 Electrochemical Cells

Chapter 18Slide 12 Electrochemical Cells

Chapter 18Slide 13 Electrochemical Cells When selecting two half-cell reactions the more negative value will form the oxidation half-cell. Consider the reaction between zinc and silver: Ag + (aq) + e –  Ag(s)E° = 0.80 V Zn 2+ (aq) + 2 e –  Zn(s)E° = – 0.76 V Therefore, zinc forms the oxidation half-cell: Zn(s)  Zn 2+ (aq) + 2 e – E° = – (–0.76 V)

Chapter 18Slide 14 Electrochemical Cells Q1. How does salt bridge complete the circuit? Q2. What is electrode potential? Q3. In electrochemical cell, why is anode negative and cathode positive? Q4. Which factors are required to form an efficient cell?