Question

What is the Keq equation?

Answer 1

For the reaction, `A+BrightleftharpoonsC+D` `;K_"eq"=([C][D])/([A][B])`.

Explanation:

`K_(eq)=([C][D])/([A][B])`

Given `A+BrightleftharpoonsC+D`, there is a `"rate forward"`, `k_f[A][B]`, and a `"rate backwards"`, `k_r[C][D]`; `k_f` and `k_r` are some unspecified rate constants.

Equilibrium, by definition, explicitly specifies EQUALITY of FORWARD and REVERSE rates, and thus:

`k_f[A][B]=k_r[C][D]`;

Under these conditions, chemical change has not ceased, but there is no net macroscopic change in the given concentrations.

Further we can write, `k_f/k_r=([C][D])/([A][B])`, and this is usually specified under standard conditions.

The quotient `k_f/k_r` is better as known `K_"eq"`, the thermodynamic equilibrium constant, and it must be measured for a given reaction.