Equilibrium Constant in terms of Molar Concentration of Gases versus Equilibrium Constant Suppose the gases involved in a reaction behave as real gases with
significant intermolecular attractions. 

I just learned that $$K_c(RT)^{\Delta n_r} = K$$

Would the value of Kc calculated
from the equation above be too high, too low, or the same as the actual value?

I thought that it would be the same, but I don't think that's right because deviation from ideal behavior should deviate from equilibrium.
I believe that the real $K_c$ would be higher. This is because in ideal gases london dispersion forces, hydrogen bonding, etc. is ignored. These would increase the number of collisions between particles since they would be attracted to each other more.
$$\ce k=zp*e^{-E_a/RT}$$
where k= rate constant, z= frequency of collisions, p= fractions of collisions with proper orientation to cause a reaction, $E_a$= activation energy, T= temperature. So Since z would increase, the K would increase. Hence the $K_c$ would increase.