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

2021
Views:

269

Pages:

2
Author:

Heath Myers

Study Guide to Electrochemistry 1. Term to know: • Faraday Constant: The charge (in Coulombs) of one mole of electrons: F = 96485 C / mol e2. The relationship between ΔG and Ecell: ΔG = -nFEcell • Where: o ΔG: Change in Gibbs Free Energy o n: number of moles of electrons exchanged in the redox reaction o F: Faraday’s constant o Ecell: The general cell potential (not necessarily under standard conditions) 3. How to tell if a reaction is spontaneous from the value of Ecell: • If Ecell is positive (Ecell > 0), then the reaction is spontaneous • If Ecell is negative (Ecell < 0), then the reaction is not spontaneous 4. How to combine known E° values to find an unknown E° value Consider the following reaction: Fe3+(aq) + 3e- -> Fe(s) This reaction (and its E° value) are not found in the standard reduction potentials table. Instead, we find the following: 1. Fe2+(aq) + 2e- -> Fe(s) (E° = -0.440 V) 2. Fe3+(aq) + e- -> Fe2+(aq) (E° = 0.771 V) 3. Fe3+(aq) + 3e- -> Fe(s) (E° = ?) We cannot just add the E° values because the number of electrons transferred is different for both equations. Instead, we calculate the ΔG values, which we can then add: ΔG = -nFE°cell 1. ΔG = -(2 mol e-)(96485 C/mol e-)(-0.440 V) = 0.880F V 2. ΔG = -(1 mol e-)(96485 C/mol e-)(0.771 V) = -0.771F V ΔGtotal = 0.880F V – 0.771F V = 0.109F V We can then use ΔGtotal to calculate E°: ΔGtotal = 0.109F V -nFE° = 0.109F V -3FE° = 0.109F V E° = -0.0363 V

Study Guide for Electrochemistry 2

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