The Chemical Reaction Mechanism

Greetings,

This post discusses the concept of the reaction mechanism.  

Every chemical reaction actually occurs as a series of individual, smaller reaction steps.  A listing of these reaction steps (aka Elementary Reactions) is called the mechanism of a chemical reaction.  The mechanism is the pathway of a chemical reaction.  A reaction mechanism will show intermediates (short-lived products which appear as reactants in other mechanism steps).

Adding Mechanism Steps

The reaction mechanism can be thought of as individual steps added together.  The sum-total of these steps yields the actual (or total) chemical equation of the reaction.  The concept of adding mechanism steps to produce the total reaction is a result of Hess's Law (Named after the Swiss-Born Russian Chemist, Germain Hess, who published his findings in 1940).  Hess's Law tells us that the Enthalpy (aka Heat) of a Reaction can be calculated from the sum-total of enthalpies of reaction mechanism steps.  A result of Hess's Law is the concept of the reaction mechanism.  If the overall reaction enthalpy is the sum-total of elementary-reaction-enthalpies, then the chemical reaction itself can be thought of as the sum of the individual elementary-reactions.  The following figure shows a reaction mechanism for a hypothetical chemical process.

The figure shows that intermediate compounds will cancel to yield the total reaction equation.  Also indicated, is the fact that an overall reaction product can appear as an intermediate compound.

That's all for this post.

Have a good one!

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