Equilibrium Concentration vs Pressure

[Mona El Masri 1F]

Given a reaction, how do you know whether to write an equation for pressure or concentration? How do we know when to use Kc or Kp given just a reaction?

[Patrick Cai 1L]

If a reaction is given with reactants and products solely in the gas phase, we would use K_p and use partial pressures derived from concentrations and the ideal gas law. Otherwise, K_c would be used with the concentrations involved.

[Mona El Masri 1F]

There was a problem that consisted of only gases but the concentration was used....

[marisaimbroane1J]

This will most likely depend on the information given in the problem and what is asked for. For reactions with all gases, it is possible to use either concentrations or partial pressures.

[sallina_yehdego 2E]

It depends on the information given in the problem. It will most likely ask for you to find either or.

[gwynlu1L]

I believe that if the question gives you concentrations of gases and asks for Kc and doesn't specify to find Kp instead, you can still find Kc instead of converting to partial pressures to find Kp. Only if the question specifies to find the Kp if given the concentrations would you probably have to convert the concentrations to partial pressures.

[Clarissa Cabil 1I]

Setting up the equation to find the equilibrium constant of a reaction, is essentially the same concept for both K_C and K_P.

When given aA + bB ⇌ cC + dD,

K_C= [C]^c[D]^d / [A]^a[B]^b

K_P= (P_C)^c(P_D)^d / (P_A)^a(P_B)^b

However, your answer will depend on what the question is asking you to find.