Question

For an equilibrium reaction, how can `K_c`, and `K_P` be related?

Answer 1

`K_c`, requires units of concentration in `mol*L^-1`; `K_p` units pressure. The constants can be related.

Explanation:

For the reaction,
`A + B rightleftharpoons C+ D`, we can write the equilibrium constant in terms of concentration, `mol*L^-1`:
`K_c` `=` `([C][D])/([A][B])`

Note that `K_c` is dimensionless. Should the reaction be in the gas phase, then we can utilize the Ideal Gas Law: `PV=nRT`, or `n/v = P/(RT)`. Dalton's Law of partial pressures holds that the pressure exerted by a component in a gaseous mixtures is the same as the pressure it would exert if it alone occupied the container, thus,

`n_A/v = P_A/(RT)`; `n_B/v = P_B/(RT)` etc.

And `K_P` `=` `([P_C][P_D])/([P_A][P_b])` `=` `K_c/(RT)`

Reasonably, ideal gas behavious is assumed. So, the units can be in `mol*L^-1`.