[envanyatar]

For Kc do you include solids/liquids/gases?
For Kp do you include solids/liquids/gases?

[Donaldson Tan]

both Kc and Kp exclude solid because the concentration of solid (ie. its density) is effectively a constant

[envanyatar]

What about liquids? do Kc include liquids?

[hmx9123]

What does your sentence mean, geo?  I can't figure it out.

[Donaldson Tan]

the reason why we exclude solid concentration in the equilibrium expression is because solid concentration is effectively its density. Its density remains constant throughout the equilibrium state, despite any disturbances. even if the number of moles of solid changes during an isothermal process, the concentration (ie. density) remains unchanged. It wont contribute to the changes in molar concentration of other species.

[yl88]

Kc involves anything with concentration. (c in Kc stands for concentration.) thus it involves liquid and gas.
Kp involves pressure, thus it only applies for gases.
Kp=Kc (RT)^delta n
R=0.0821 L atm mol^-1 K-1
T=temperature
delta n=moles product gas - moles reactant gas

[sdekivit]

pure liquids and pure solids are exluded since they are constant as geo explained. Solvents are thus exluded.

[xiankai]

after doing a search for kp and kc i stumbled on this age-old post so i guess i'll *Ignore me, I am impatient* this up instead of creating a new one, i mean god knows our forum could use a break from so many threads 

my question is that,

as K_c is applicable to liquids and gases, does that mean a gaseous reaction will have the same K_c as a liquid reaction?

for example this reaction...

N₂ (g) + 3 H₂ (g) --> 2 NH₃ (g)

now under high pressure and low temperature (-edit- changing the temperature would change the K value anyway) to liquefy the reactants and products as in the haber process (well maybe the reactants arent liquefied but lets say in a hypothetical scenario that they are all subjected to conditions that liquefy all of them), we have

N₂ (l) + 3 H₂ (l) --> 2 NH₃ (l)

instead.

will the K_c value be different for both?

also, is there any significance of raising the concentrations/partial pressures to the power of their stoichiometric ratio, apart from giving a certain variable more 'weight' in the equation?

[xiankai]

i asked my teacher and it seems that the equation with gaseous reactants/products is different from the one with liquid reactants/products, stemming from the fact that the total volume of the container is now reduced to the total volume of the liquid. hence there are 2 different K_c values.

is this a plausible explanation?