This module expands our discussion of redox into a more practical introduction to electrochemistry. How are redox reactions harnessed to store energy in batteries or used to produce electricity in fuel cells? What is corrosion and how can it be foiled? This material is covered in Chapter 20 of Brown.
Lecture 5 Topics [Brown chapter 20]
1. The half-equation approach allows us to identify oxidizing and reducing agents, to quantitate electrons involved, and the amount of acid and
solvent involved in redox reactions.
2. Batteries are self-contained electrochemical power sources, driven by spontaneous redox reactions.
a. Oxidizing agents are reduced when they remove electrons from agents they are oxidizing.
b. Reducing agents are oxidized when they donate electrons to agents they are reducing.
c. Voltaic cells each contain one half-reaction and are connected by wires for electron flow and salt bridges for the counter-flow of soluble
d. In order to create effective batteries, half-cell equations must have a positive electromotive force (Ecell) potential sum.
e. Fuel cells are open voltaic cells that convert about 70% of chemical energy into electricity.
f. Corrosion is a spontaneous, but undesirable, redox reaction that eats away at metals.
g. Electrolysis is a non-spontaneous redox reaction driven by the input of electricity.
i. Add protons and water to balance half-equations when redox reactions are conducted in acidic aqueous solutions.
ii. Voltaic cell redox reactions are spontaneous if and when the two voltaic cells are linked.
iii. The metal of the anode ‘disappears’ because oxidation turns elemental atoms into soluble ions.
iv. The metal of the cathode is added to when soluble metal ions are reduced and deposit onto the surface of the cathode.
v. Counter-ion flow keeps voltaic cells electrically neutral. Positive counter-ions flow toward the cathode and negative counter-ions
flow towards the anode.
vi. The porous membranes of fuel cells are permeable to protons but not to electrons; the membranes act a salt bridge.
vii. Corrosion only occurs if the summed Ecell value is positive, indicating spontaneous redox.
viii. The corroded metal is the anode and the oxidant is the cathode.
ix. Acid speeds corrosion by supplying hydrogen for reduced oxygen to combine with, forming water.
x. Corrosion can be prevented by covering susceptible metal surfaces, or by…
xi. Galvanization of a susceptible metal with a more easily oxidized sacrificial anode.
xii. Electrolysis is used to recover metals from solutions or to plate base metal.
Links and items of interest:
Resources for students: