Question

Using fundamental thermodynamics, and ignoring reaction kinetics, explain which of the following materials is most susceptible to corrosion in fully aerated (O2 saturated) seawater (pH = 6.5) -- aluminum metal, iron metal, glass (silicon dioxide), or gold.

Answer 1

answer:chemical corrosion is in which the metal is converted into its oxide when the metal is exposed to a reactive gas or non-conducting liquids

Corrosion may be defined as a destructive phenomena, chemical or electrochemical, which can attack any metal or alloy through reaction by the surrounding environment and in extreme cases may cause structural failure. Corrosion can be also defined as the deterioration of material by reaction to its environment. The corrosion occurs because of the natural tendency for most metals to return to their natural state; e.g., iron in the presence of moist air will revert to its natural state, iron oxide

Thermodynamic indicates the spontaneous direction of a chemical reaction. It is used to determine whether or not corrosion is theoretically possible. There is thus a fundamental thermodynamic tendency for metal to return to a stable state through corrosion processes. Thermodynamics is concerned with energy states. The original metallic ores are said to be in a state of low energy

For a reaction to be occurred spontaneously there must be a free energy change, G, and since the energy, in the case of spontaneous reaction, is given out, the sign is negative. The magnitude of the G and its sign are of great importance, since it indicates whether or not the corrosion reaction will take place

Iron metal is the most susceptible to corrosion in fully aerated and seawater condition because the free energy    ​G change associated with the change of iron metal to its corrosive form is greater ( more -ve ) compare to others corrosive metals ( aluminium, glass or gold) forms.

reaction

4Fe + 3O₂ + 2H₂O    2Fe₂O₃.H₂O

iron oxygen water hydrated Iron(III)oxide