Electrochemistry I
- 1. Dr. Khadija Munawar Assistant Professor Department of Chemistry, School of Natural Sciences, National University of Sciences and Technology(NUST), Islamabad Course Code: CH-380 Course Title: Physical Chemistry-I BS-Chemistry ( Semester V)
- 3. An Introduction to Electrochemistry Branch of science which deals with the study of all physical and chemical processes which can be carried out by electrical energy and the processes which proceed with the generation of electricity. Electrochemistry is concerned with the conversion of electrical energy into chemical energy in electrolytic cells as well as the conversion of chemical energy into electrical energy in galvanic or voltaic cells.
- 4. An Introduction to Electrochemistry Electrochemical cell: An electrochemical cell is a device that can produce electrical work in the surroundings. For example, the commercial dry cell is a sealed cylinder with two brass connecting terminals protruding from it. One terminal is stamped with a plus sign and the other with a minus sign. If the two terminals are connected to a small motor, electrons flow through the motor from the negative to the positive terminal of the cell. Work is produced in the surroundings and a chemical reaction, the cell reaction, occurs within the cell.
- 5. An Introduction to Electrochemistry Electrochemical cell: Two types 1. In an electrolytic cell, a process called electrolysis takes place. In this process, electricity is passed through a solution or the fused state of electrolyte. The electricity provides sufficient energy to cause an otherwise non-spontaneous oxidation- reduction reaction to takes place. 2. In a galvanic cell/voltaic cell, electricity is produced results from a spontaneous oxidation- reduction reaction taking place in a solution.
- 6. An Introduction to Electrochemistry Electrochemical cell: Components: An electrochemical cell consists of two electrodes, or metallic conductors, in contact with an electrolyte, an ionic conductor. An electrode and its electrolyte comprise an electrode compartment. The two electrodes may share the same compartment. If the electrolytes are different, the two compartments may be joined by a salt bridge, which is a tube containing a concentrated electrolyte solution (for instance, potassium chloride in agar jelly) that completes the electrical circuit and enables the cell to function.
- 7. An Introduction to Electrochemistry Electrochemical cell: 1. Electrolytic cell The process of electrolysis is carried in an apparatus called the Electrolytic cell. The cell contains water-solution of an electrolyte in which two metallic rods (electrodes) are dipped. These rods are connected to the two terminals of a battery (source of electricity). The electrode connected to the positive terminal of the battery attracts the negative ions (anions) and is called anode. The other electrode connected to the negative end of the battery attracts the positive ions (cations) and is called cathode.
- 8. An Introduction to Electrochemistry Electrochemical cell: 1. Electrolytic cell
- 9. An Introduction to Electrochemistry Electrochemical cell: 1. Electrolytic cell Examples: Downs cell: Extraction of sodium by the electrolysis of fused sodium chloride is carried out. Nelsons cell: Caustic soda (NaOH) is obtained by the electrolysis of concentrated aqueous solution of sodium chloride.
- 11. Electrochemical cell: Two types
- 12. An Introduction to Electrochemistry Electrochemical cell: 2. Galvanic/Voltaic cell When a spontaneous reaction takes place in a galvanic cell, electrons are deposited in one electrode (the site of oxidation, the anode) and collected from another (the site of reduction, the cathode), and so there is a net flow of current which can be used to do work. Note that the + sign of the cathode can be interpreted as indicating the electrode at which electrons enter the cell, and the sign of the anode is where the electrons leave the cell.
- 13. An Introduction to Electrochemistry Electrochemical cell: 2. Galvanic/Voltaic cell In a galvanic cell, the cathode has a higher potential than the anode: the species undergoing reduction, withdraws electrons from its electrode (the cathode), so leaving a relative positive charge on it (corresponding to a high potential). At the anode, oxidation results in the transfer of electrons to the electrode, so giving it a relative negative charge (corresponding to a low potential).
- 14. An Introduction to Electrochemistry Electrochemical cell: 2. Galvanic/Voltaic cell: Daniel Cell One version of the Daniell cell. The copper electrode is the cathode and the zinc electrode is the anode. Electrons leave the cell from the zinc electrode and enter it again through the copper electrode.
- 15. Activity Compare electrolytic and galvanic cell in terms of similarities and dissimilarities
- 16. The reducing agent (or reductant) is the electron donor; The oxidizing agent (or oxidant) is the electron acceptor; Any redox reaction may be expressed as the half-reactions. As the reaction proceeds, the electrons released in the oxidation Red1 Ox1+ 僚e at one electrode travel through the external circuit and re-enter the cell through the other electrode. There they bring about reduction Ox2+ 僚e Red2. The reduced and oxidized species in a half-reaction form a redox couple. In general we write a couple as Ox/Red and the corresponding reduction half-reaction as Ox+ 僚e Red For example In the Daniell cell, the redox couple at one electrode is Cu2+/Cu and at the other is Zn2+/Zn
- 17. Cell notation: Explanation and examples will be discussed in class on board