Writing equilibrium constants for reactions with multiple phases

[samy4408]

Hello we learned about the chemical equilibrium and how to write it's formula in the case of liquid and gaseous phase , what about a reaction involving different phases ? like this one : how do we write the formula for the chemical equilibrium ? do we just ignore the carbon ,is there any rules to write the chemical equilibrium that i forgot ?

 

[Borek]

Activity of solids is assumed to equal 1.