Regarding Ellingham diagrams

In my textbook, the following information is given about Ellingham diagram:

The interpretation of $$\ce{\Delta_rG^\circ}$$ is based on $${K}$$ ($$\ce{\Delta G^\circ = -RTlnK}$$). Thus it is presumed that the reactants and products are in equilibrium:

$$\ce{M_xO + A_r_e_d <=> xM + A_r_e_dO}$$

This is not always true because the reactant/product may be solid. In commercial processes, reactants and products are in contact for a short time.

I am not able to understand why this is not always true. How does the reactant or product being solid determine if the equilibrium will be reached or not? (Presence of solid doesn't even influence the value of K as it's activity is always taken as 1.)

Also, what does the fact that "reactants and products are in contact for a short time" signify? Do they mean that due to less time of contact, the equilibrium will not be reached (because it takes some time to attain it)?

• In the case of "short time," your interpretation is correct. The rest is a little ambiguous. May 29, 2021 at 11:00