Equilibrium Constant

[RobinFong_2B]

I noticed the answers to the questions in the textbook that ask for the equations of K for a chemical equation in equilibrium give their answers using the partial pressure of products and reactants. Should we assume that when asked for K, they are referring to K sub p and not K sub c, where we would give our answer in concentration?

[Lara Almeida 3D]

I had the same question but from what I understand given the textbook problems, if all the elements in the reaction are gases you should use Kp, and if there are elements in aqueous form you use Kc. But in the exam I think Dr Lavelle will be more explicit about what he expects us to use.

[Irene Kim 3E]

Professor Lavelle mentioned in lecture that if all of the products and reactants involved in the equilibrium reaction are gases, we can use K_p (and subsequently write the expression for equilibrium as P_products/P_reactants). If we're using K_c, the expression becomes [products]/[reactants] - though either way, you'd end up with the same K values.

[Madeline Ellmore 2C]

Adding on to Irene's point, he also said look at what is given initially. If the units are in "bar" or "atm" use Kp and if they're in "mol" or "M (molar)", use Kc.