University:
Santa Ana College
Course:
CHEM 229 | General Chemistry and Qualitative Analysis
Academic year:

2021
Views:

119

Pages:

2
Author:

Alexia Bell

Study Guide for CHEM 219/229 How to write a redox reaction using Electrochemical Cell notation: Terms to know: • • • • • • • Redox Reaction: A chemical reaction that involves the transfer of electrons between species, with one species losing electrons (being oxidized) and another species gaining electrons (being reduced). Electrode: For the purposes of electrochemistry, a strip of metal. Half- cell: An electrode submerged in a solution of ions of the same metal. Electrochemical Cell: Two properly connected half cells. Two kinds: Galvanic and electrolytic o Galvanic Cell: An electrochemical cell that uses a chemical reaction to produce electrical energy. o Electrolytic Cell: An electrochemical cell that uses electrical energy to drive a chemical reaction. Anode: The half-cell where oxidation takes place. Cathode: The half-cell where reduction takes place. Salt-bridge: A porous barrier (generally a U-tube) that allows ions to move between half-cells to complete the electrical circuit. General Cell Diagram: Electrode|Solution||Solution|Electrode • • • • The single lines represent the phase boundary between each electrode and its solution The double lines represent the salt bridge The anode is always written on the left of the diagram, the cathode always on the right. Example: o For the following reaction: Mg (s) + FeCl2 (aq) -> Fe (s) + MgCl2 (aq) o o o o o We start by assigning oxidation numbers: Mg (s):  Mg O.N = 0 FeCl2 (aq):  Fe O.N = +2  Cl O.N = -1 Fe(s):  Fe O.N = 0 MgCl2 (s)  Mg O.N = +2  Cl O.N = -1 We can see that the Mg is being oxidized (it goes from a 0 to a +2 O.N), while the Fe is being reduced (goes from a +2 to a 0 O.N). We can then break the redox reaction into half-reactions. One reduction half-reaction and one oxidation half-reaction: o • Red: Mg (s) -> Mg2+ (aq) + 2eOx: Fe2+ (aq) + 2e- -> Fe (s) • • Notice that the Cl does not appear. Because it doesn’t change during the reaction, it is only a spectator ion and can be ignored. Each of these half reactions can then be written as a half-cell, with the oxidation half-reaction being at the anode and reduction half-reaction being at the cathode: Anode|Solution||Solution|Cathode Fe(s)|Fe2+(aq)||Mg2+(aq)|Mg(s)

Study Guide for Electrochemistry 6

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