Electrochemical Cells, Corrosion, and Nuclear Reactions

Electrochemical Cells: Batteries and Redox

In a voltaic pile, a spontaneous redox reaction produces energy. Conversely, in an electrolytic cell, a redox reaction occurs only when external energy is provided.

Commercial Battery Types

• Primary Batteries: Reactants are consumed during the reaction; once depleted, the battery is exhausted.
• Secondary Batteries: These are rechargeable; the reaction can be reversed by applying an external current.
• Fuel Cells: Combustion occurs via redox reactions, with hydrogen-oxygen (H₂-O₂) cells being the most common.

Corrosion of Iron

An iron plate undergoing corrosion shows specific areas where the metal is attacked. Corrosion accelerates under the following conditions:

• Contact with seawater.
• Presence of a strong electrolyte.
• Wet storage conditions.

Electrochemical Heterogeneities

Corrosion is initiated by heterogeneities, as a perfectly homogeneous metal in a uniform medium would experience minimal corrosion. Factors include:

• Compositional differences: Variations in the metal phase or the surrounding medium.
• Oxygen concentration: Differences in oxygen levels across the metal surface.

Protective Coatings

Coatings can be metallic or non-metallic. When using a sacrificial metal shield, it must have a lower oxidation potential than the metal it protects. If the coating is scratched, the protective metal will oxidize instead of the base metal.

Differences Between Ordinary and Nuclear Reactions

1. Atomic Structure: Ordinary reactions involve bond breaking and formation; nuclear reactions involve the transformation of atoms into different elements.
2. Particles Involved: Ordinary reactions involve electrons, while nuclear reactions involve protons and neutrons.
3. Energy Exchange: Ordinary reactions involve small energy changes, whereas nuclear reactions release enormous quantities of energy.
4. Reaction Rates: Ordinary reactions are affected by pressure and temperature, while nuclear reactions are not.

Nuclear Fission and Fusion

Nuclear Fission

Fission occurs when a heavy nucleus (mass > 200) is bombarded by neutrons. It breaks into smaller, more stable nuclei, releasing additional neutrons and significant energy. Uranium and plutonium are the primary elements of interest.

Nuclear Fusion

Fusion occurs when small nuclei join to form a larger nucleus. These reactions require extremely high temperatures and are known as thermonuclear reactions, which are the processes that power the sun.