Kp or Kc

[705170809]

How do you know when to use Kp or Kc? If the question does not specify, can you use either?

[Maddy Mackenzie]

typically if the question gives you a concentration then you would use Kc and if it gave you pressure then you would use Kp. You only use Kp if there are all gases in the reaction so if there are aqueous solutions involved then you need Kc. I believe you technically can use either if the question does not specify but there will typically be one that is easier to use and you will not have to convert many measurements to use.

[Shubham Rai 2C]

I agree, typically use Kc for aqueous solutions while Kp for gases. You can also convert Kp to Kc using the equation Kp = Kc [RT]^ng, where ng is the sum of the constants of products and reactants.

[Michael Novelo 4G]

often times Kp will be used when the reaction involves gases and ask for the partial pressure. If the question is asking for molar concentration automatically assume to use Kc. Also remember when using Kc use brackets which indicate concentration and for Kp use parentheses to indicate partial pressure. (When setting up to solve for either Kp or Kc) Kp and Kc are essentially the same thing (K) so if the question isn't asking for specific partial pressure or concentration use the context that it's given to help you figure out which equation/K you can use