When does chemical equilibrium result?

1 Answer
anor277
Aug 30, 2016

When the forward rate is equivalent to the reverse rate of reaction.

Explanation:

For the equilibrium, #A+BrightleftharpoonsC+D#,

There is a rate forward, #=# #k_f[A][B]#,

And there is a reverse rate, #=# #k_r[C][D]#.

By definition, chemical equilibrium occurs when the forward rate is equivalent to the reverse rate:

#k_f[A][B]# #=# #k_r[C][D]#.

And thus, #([C][D])/([A][B])# #=# #k_f/k_r#

The dimensionless constant, #k_f/k_r#, is also known as #K_c#, the thermodynamic equilibrium constant. This is usually a constant for given conditions.

Large values of #K_c# clearly favour the product sides, whereas small values favour the reactant side. Much thermodynamic data have been recorded with respect to various chemical equilibria.

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