Standard Reduction Potentials Its all about ~~ SHE! U4 S2 L2 Standard Reduction Potentials Its all about ~~ SHE! Textbook Readings MHR page 761: Introducing Cell Potentials page 768: Standard Cell Potentials pages 769-774: Calculating Standard Cell Potentials Textbook Practice Items MHR page 773: items 5, 6, 7 and 8 page 774: Thought Lab page 775: items 1-4, and 6

Upon completion of this lesson, you should be able to: define half-cell voltage, standard half-cell, cell voltage, E°   use a standard reduction potential table to predict cell voltage and to predict if the redox reaction is spontaneous (occurs as it is written)   develop a table of redox half-reactions from experimental results

Electrons spontaneously flow from a position of higher potential energy (anode) to a position of lower potential energy (cathode). The moving electrons can do work; light bulbs, motors….

Electric potential of a cell: E p 761 The difference between the potential energy of the anode and the cathode. Measured in volts (V) Commonly called – cell voltage or cell potential A cell potential of 0 V (zero) means the cell has no electric potential. If the electrodes are the same, then there is no difference in there potential and will not generate any electric potential (same height) Electrodes must be different.

Standard cell potentials p 768 The standard half cell table of reduction potentials was created by comparing all half cell reactions with the standard hydrogen electrode (SHE) The SHE has H2(g) bubbled over a Pt electrode in 1.0 mol/l HCl(aq). This half cell has been given a E0 = 0.00 V.

Standard reduction potentials of half cells Table 19.1 p 768 or Table E.14 p 848 These are standard values which means: all elements in the table are in their standard states at 25oC and 101.3 kPa. And all ions have a standard molar concentration of 1.0 mol/L. Keep in mind that all half cells are written as reduction. For oxidation half reactions we need to reverse the equation and change the sign! Strongest reducing agent is lowest on the right on the table. Strongest oxidizing agent is highest on the left

Zn(s) | Zn2+(1.0mol/L) || Cu2+(1.0mol/L) | Cu(s) Calculate the Eo for the following cell: Zn(s) | Zn2+(1.0mol/L) || Cu2+(1.0mol/L) | Cu(s) Formula method: Half cell method:

Calculate the E0 for this reaction:

Zn | Zn2+(1 mol/L) || H+(1 mol/L) |Pt,H2 Which half cell will be the anode? Zn | Zn2+(1 mol/L) || H+(1 mol/L) |Pt,H2

Spontaneity – will electrons flow! p 770 If a cell is to produce an electric current the E0cell must be positive. That is, the cathode must have a higher reduction potential than the anode. Ie: On the table, the cathode must be higher on the table than the anode. Calculate the cell potential for each: Indicate if a current can be produced. Cd | Cd2+ || Cu2+ | Cu I2 | 2 I- || 2 Cl- | Cl2

Reduction table trends: Which will react spontaneously with Br2 but not with I2? Ie: On the table, the cathode must be higher on the table than the anode. Cr2+ F - Fe2+ Mn2+

P 775 #2c

P 775 #6