Using Kc vs Kp

[Nathan Barger 3B]

When exactly do you use Kc and when exactly do you use Kp. Although I understand that if you are given molar concentrations you should use Kc and if you are given partial pressures you should use Kp but if a question asks to simply write the expression for the equilibrium constant for the reaction and no numbers or concentrations are given but the gas equation is given, which do I use? I thought we were supposed to simply use Kc but the answer given in the back says to use Kp. is this because the entire equation involves nothing but gases?

[Chem_Mod]

If there are only gases then Kp is appropriate. You would only be able to use Kc if the total volume of the container were given.

[Kiara Quinn 3B]

Would there be a case in which you would have to use both Kc and Kp at the same time?

[Joshua Baysa 1J]

I don't think you would have to use both Kc and Kp simultaneously (at least for this class). I'm not 100% sure but it doesn't seem like it. However, there is a way to manipulate the formulas in order to get both Kc and Kp in the same equation