The Chemistry of Solids, Part 7 - Chemical Reactions

Greetings,

This post explains a couple common types of chemical reactions involving solids.  Examples are also provided.

A chemical reaction will likely occur when the potential products are more chemically stable than the starting materials (reactants).  We say that these types of reactions are "thermodynamically-favored".  It is important to understand that a thermodynamically-favored reaction is not necessarily a fast one.  Rate of a reaction is a function of the overall mechanism, consisting of a series of more elementary reactions which, when added together, "add up" to a complete chemical equation.  The rates of elementary reactions, while subject to some thermodynamic considerations, are also greatly affected by statistical probabilities such as collision frequency, molecular orientation, and intermediate-product stability.

Many pure metal elements are easily oxidized to form stable ionic compounds.  Redox reactions of the alkali-metal elements are particulary fascinating!  Other metals oxidize in ways which cause annoyances and sometimes outright dangerous conditions - rusting of car suspension components and steel bridge supports come to mind.

Certain solid compounds tend to decompose when the products themselves are pure stable gaseous or liquid-state compounds.  An interesting example is the decomposition reaction of ammonium carbonate.  This reaction can easily be initiated with some gentle heating: A hot water bath will do.  The entire solid breaks down into the stable products, ammonia gas, carbon dioxide gas, and water vapor.  The reaction is further driven by an increase in entropy, which relates to the energy consumed in the formation of more disordered products from highly ordered reactants.

That's all for now.
Thank you for reading.

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