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equilibrium, chemical

That composition of a chemical reaction where there is no further net change in the reaction mixture. Individual molecules continue to react, but for every forward reaction there is a compensating backward one; the equilibrium is dynamic.

The equilibrium constant for the reaction

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is defined as

K=[C]{TAG(tag=>sup)}c{TAG}[D]{TAG(tag=>sup)}d{TAG}/[A]{TAG(tag=>sup)}a{TAG}[B]{TAG(tag=>sup)}b{TAG},

where [X] represents the concentration (in more precise work, the activity should be used) of X at equilibrium. The equilibrium constant is a constant for a given reaction at a given temperature and any composition will evolve until the concentrations satisfy the equilibrium constant (K).

The equilibrium composition corresponds to the lowest Gibbs energy for the reaction. The equilibrium constant K is related to the standard Gibbs energy change by the equation

Î”GÎ˜ = -RT ln K,

where R is the gas constant and T the thermodynamic temperature.

The only way an equilibrium constant can be altered is by changing the temperature. When the temperature is increased, reactions shift in the endothermic direction (See Le Chatelier\'s principle).

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equilibrium, chemical

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equilibrium (plural equilibria)

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