Posted by Riley on Friday, September 10, 2010 at 3:12am.
I'm doing chemical equilibrium, and there's a question in my lecture notes. Can someone check my answers and tell me if i'm right or wrong? Thanks!
The Kc expression for this reversible reaction:
3Fe(s) + 4H2O (g) --><-- Fe3O4(s) + 4H2 (g)
is [H2]^4 / [H2O]^4
Am I correct? My lecture notes apparently said that the reaction has a Kp expression but it didn't say anything about Kc expression. I just thought it can also have a Kc expression, not sure if i'm right.
- Chemistry - Riley, Friday, September 10, 2010 at 3:17am
And this one too! I thought it should also have a Kc expression but my notes only mentioned the Kp expression:
( that weird arrow is the forward backward arrow for a reversible reaction)
H2(g) + Br2(l) --><-- 2HBr2(g)
Kc = [HBr]^2 / [Br][H2]
Please tell me if im right! I reasoned that there should be a Kc expression since for Kc expressions you should exclude water (when used as a solvent) and solids, so i thought that's applicable for these equations...
please help thanks!
- Chemistry - Dr Russ, Friday, September 10, 2010 at 4:57am
What is included in the Kp expression - partial pressures of the components.
The partial pressure of a solid does not change, so does not appear in Kp. This is the same with Kc as solids do not appear in Kc.
Liquids do not appear in Kp either.
- Chemistry - Riley, Friday, September 10, 2010 at 5:08am
Um. that does not answer my question of whether liquids, aqueous, and gases appear in Kc expressions or not.
- Chemistry - Dr Russ, Friday, September 10, 2010 at 6:36am
Gases appear in Kc expressions as concentrations.
In aqueous and other solvent systems the solute appears as a concentration in Kc expressions.
Pure materials such as solids and solvents (including water) do not appear in the equilibrium expression.
A substance such as water will of course appear if they are one of the products or reactants. For example in
note the gas phase.
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