Kc vs Kp

[Sid Panda 3A]

When they are calculated, are Kc and Kp the same value? I know one deals with concentration while other deals with pressures. I was curious if the values turn out the same.

If they aren't the same, then what would we use each equilibrium constant for?

[Evie Li_1H]

Kc is the equilibrium constant given by the terms of concentration whereas Kp is the equilibrium constant given by the terms of pressure. You only use Kp when you're dealing with gases since liquids and solids don't necessarily change pressure, but gases can be compressed. Both should be calculated the same way, it's just a matter of labeling your answer correctly I believe.

[Ivy Tan 1E]

Hi! I think the Kc and Kp values are the same once they're calculated out. The only difference is when calculating Kc, you use the concentrations of each molecule and when calculating Kp, you use the partial pressures of each gas. Hope this helps!!

[Andrew Wang 1C]

While Kc and Kp are calculated the same way, I don't think they are equal in value. Kp can be used if the reaction involves only gases, while Kc can be used for gases and aqueous solutions. The problem will usually tell you which one to solve for by looking at the units (moles for Kc, atm or bar for Kp).

[Joey_Okumura_1E]

Kc uses the equilibrium molar concentrations while Kp uses the equilibrium partial pressures. Their values will be different. Kp = Kc(RT)^(delta n)

[Jessica Katz]

I believe that you will end up with two different values for the kp and the kc its just a matter of what numbers you are plugging into the k expression. When it is kp, all of the values will be converted to the partial pressure and for kc, the values need to be in terms of concentration. It will result in the same findings, like determining whether the forward or reverse reaction is favored, but the actual values will be different because different values are being plugged in and manipulated.

[Charlotte Adams 1A]

I believe the values will be different but if you need to convert one to the other you can use the equation PV=nRT.

[Xinying Wang_3C]

Kc is about the molar equilibrium concentration, Kp is the equilibrium partial pressure, and they are two different values.

[Jamie Wang 3C]

The values are different because one is talking about the concentration (mol/L) of each component, while the other is talking about the pressure.

To convert use PV=nRT

P = (n/V)RT

n/V = concentration because it is amount over volume (ex: mols/liters)

[Kimiya Aframian IB]

When they are calculated, are Kc and Kp the same value? I know one deals with concentration while other deals with pressures. I was curious if the values turn out the same.

If they aren't the same, then what would we use each equilibrium constant for?

Hi! The Kc and Kp values are calculated in the same way, except the final answer for Kc is concerning concentration while Kp is concerning pressure. It is important to note that Kp is usually used in reactions where there are only gases. Hope this helps!

[Grecia Velasco 1G]

From my understanding:
Kc is for concentrations (mol.L^-1) and Kp is for pressure (bars). The thing is, gases can also be calculated with concentrations so it can use Kc and Kp it just depends what you're given.
If this is incorrect someone please tell me haha.

[Katie Le 3K]

Both are calculated the same way. Kc uses concentration Kp uses pressure.

[Adrienne Yuh 2B]

Calculation wise, both use the same steps except Kc is using concentration and Kp is pressure.

[Vivian_Le_1L]

In terms of steps, I believe it's the same K = [product]/[reactant], but Kc uses concentration and Kp uses partial pressure. You can use PV=nRT to convert concentration to pressure and vice versa. Also, Kp is only for gases, while Kc is for gases and aqueous solutions. I think the values will be different depending on which one you're looking for.

[JaesalSoma1E]

Kc refers to the equilibrium constant in concentration problems and Kp refers to the equilibrium constant in pressure problems