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### Equilibrium Concentration vs Pressure

Posted: Mon Jan 07, 2019 5:31 pm
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?

### Re: Equilibrium Concentration vs Pressure

Posted: Mon Jan 07, 2019 5:49 pm
If a reaction is given with reactants and products solely in the gas phase, we would use Kp and use partial pressures derived from concentrations and the ideal gas law. Otherwise, Kc would be used with the concentrations involved.

### Re: Equilibrium Concentration vs Pressure

Posted: Mon Jan 07, 2019 7:48 pm
There was a problem that consisted of only gases but the concentration was used....

### Re: Equilibrium Concentration vs Pressure

Posted: Mon Jan 07, 2019 8:34 pm
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.

### Re: Equilibrium Concentration vs Pressure

Posted: Mon Jan 07, 2019 11:13 pm
It depends on the information given in the problem. It will most likely ask for you to find either or.

### Re: Equilibrium Concentration vs Pressure

Posted: Tue Jan 08, 2019 1:29 am
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.

### Re: Equilibrium Concentration vs Pressure

Posted: Tue Jan 08, 2019 12:11 pm
Setting up the equation to find the equilibrium constant of a reaction, is essentially the same concept for both KC and KP.

When given aA + bB ⇌ cC + dD,

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

KP= (PC)c(PD)d / (PA)a(PB)b