January 22, 2021, 10:16:33 AM
Forum Rules: Read This Before Posting


Topic: Writing Kp and Kc for heterogeneous equilibrium  (Read 7724 times)

0 Members and 1 Guest are viewing this topic.

Offline Corribus

  • Chemist
  • Sr. Member
  • *
  • Posts: 3025
  • Mole Snacks: +458/-22
  • Gender: Male
  • A lover of spectroscopy and chocolate.
Re: Writing Kp and Kc for heterogeneous equilibrium
« Reply #15 on: June 08, 2013, 03:22:31 PM »
I'm getting a little confused by what the question is, exactly.  Could you restate it explicitly?
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline Big-Daddy

  • Sr. Member
  • *****
  • Posts: 1177
  • Mole Snacks: +28/-94
Re: Writing Kp and Kc for heterogeneous equilibrium
« Reply #16 on: June 08, 2013, 03:51:04 PM »
I'm getting a little confused by what the question is, exactly.  Could you restate it explicitly?

My question was - "Is it correct to suggest that a liquid species itself contributes to the pressure of a system, only through conversion into the gaseous state as per a vapour-liquid equilibrium, wherein the gaseous phase species then exerts a partial pressure and behaves just like any other gas, i.e. we sum its partial pressures up with those of the other gases to calculate the total pressure. In other senses the liquid does not affect the pressure or have a gaseous partial pressure for obvious reasons."

Needask's question as I interpret it was - "If the vapour-liquid equilibrium A (l)  ::equil:: A (g) is established, to some extent, for any liquid, then shouldn't placing A (g) alone in a container lead to the production of A (l) to meet the equilibrium constant (just as placing A (l) in a beaker will lead to the production of A (g))?"

Offline Needaask

  • Full Member
  • ****
  • Posts: 186
  • Mole Snacks: +6/-16
Re: Writing Kp and Kc for heterogeneous equilibrium
« Reply #17 on: June 09, 2013, 03:54:44 AM »
I'm getting a little confused by what the question is, exactly.  Could you restate it explicitly?

Oops sorry about that I think I went a little off in my questions. The question I just asked was from BD's side questions.

 For Kp we would use the partial pressure of the products and reactant. So the reason we don't include them is at they are constant at a specific temperature. However, I was thinking at the equilibrium of the reaction, won't the partial pressure of everything be constant?

But say there's a change in the equilibrium and temperature remains the same. So now even the amount of solid or liquid changes. So shouldn't their (solids and liquids) pressure change as well and not just the gas as the partial pressure is dependent on the mole fraction of the liquids something like Raoult's Law?

Then for Kc, we would use concentrations. And similarly isn't everything constant at equilibrium? But again if there is a change in equilibrium changing the amount of everything then shouldn't the concentration of the solids and liquids change as well and not just the aqueous and gaseous?

My idea of concentration would be number of moles of solute/volume of solution. So if I out in 10 moles of a solid into 100cm3 of water, the concentration would be 10mol/volume of solid+water. So by this shouldn't the concentrations change as the volume isn't only the volume of the solid but now it includes the volume of the water too. Also from this chemguide link I also have some doubts (http://www.chemguide.co.uk/physical/equilibria/kc.html#top) in the examples they used concentration of the liquids (not aqueous or gaseous here) so if they were to explain the usual solids and liquids have a fixed concentration, then wont all their concentrations be fixed no matter what happens which makes this equation not make sense?

So I'm quite confused about this whole Kc and Kp thing. Thanks Corribus :)
« Last Edit: June 09, 2013, 05:01:17 AM by Needaask »

Sponsored Links