Equilibrium Concentration vs Pressure

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Mona El Masri 1F
Posts: 34
Joined: Fri Sep 28, 2018 12:20 am

Equilibrium Concentration vs Pressure

Postby Mona El Masri 1F » 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?

Patrick Cai 1L
Posts: 93
Joined: Fri Sep 28, 2018 12:25 am

Re: Equilibrium Concentration vs Pressure

Postby Patrick Cai 1L » 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.

Mona El Masri 1F
Posts: 34
Joined: Fri Sep 28, 2018 12:20 am

Re: Equilibrium Concentration vs Pressure

Postby Mona El Masri 1F » Mon Jan 07, 2019 7:48 pm

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

marisaimbroane1J
Posts: 69
Joined: Fri Sep 28, 2018 12:23 am

Re: Equilibrium Concentration vs Pressure

Postby marisaimbroane1J » 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.

sallina_yehdego 2E
Posts: 75
Joined: Sun Apr 29, 2018 3:00 am

Re: Equilibrium Concentration vs Pressure

Postby sallina_yehdego 2E » 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.

gwynlu1L
Posts: 62
Joined: Fri Sep 28, 2018 12:19 am

Re: Equilibrium Concentration vs Pressure

Postby gwynlu1L » 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.

Clarissa Cabil 1I
Posts: 66
Joined: Fri Sep 28, 2018 12:19 am

Re: Equilibrium Concentration vs Pressure

Postby Clarissa Cabil 1I » 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

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


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