Equilibrium

In contrast to the simple case of two competing irreversible reactions (previous topic), many organic reactions consist of competing equilibria, and the outcome in such cases may not be immediately obvious.
If all steps are reversible, the thermodynamically favored (most stable) species will eventually predominate, even though certain intermediate species may be formed along the way. For example, the people visiting a Natural History Museum will be distributed among the various rooms and exhibits in a dynamic fashion. Some exhibits, such as dinosaurs and space exploration, will on average be more highly populated than others, but people can move easily from one site to another. If an incentive (or driving force) is introduced (such as free snacks in the cafeteria) most of the visitors will move to this desireable (more stable) location.
If an essentially irreversible step is introduced among many reversible steps, the transformation induced by this step will eventually divert all the initial and intermediate molecular species to its product. Thus, at closing time the visitors to our Museum pass through exit doors and are prevented from reentering.

For an animated illustration of how a system of competing and sequential reversible reactions might behave Click Here

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