K vs. Kc

[Samantha Pedersen 2K]

Some of the textbook problems for Outline 1 ask us to refer to Table 5G.2 to find the equilibrium constant for a certain reaction and use it to solve the problem. For each reaction, there is a K value and a Kc value listed in Table 5G.2 and I've noticed that the two values are sometimes different. How do we know when to use K and when to use Kc? Thank you!

[Anirudh Mahadev 1G]

In my understanding, K and Kc are almost interchangeable, but K is more general, while Kc is mainly used in the context of comparing concentrations. K can be used to cover both the equilibrium constant of concentrations, Kc, and the equilibrium constant of gas pressures, Kp. Dr. Lavelle with probably explain the difference more in detail in Wednesday's lecture when he explains how to calculate Kp. Hope this helps!

[Madeline Ogden 3B]

I agree with the post above! K is a broad term for all equilibrium constants whereas Kc is a more specific term for equilibrium constants dealing with concentration.

[Sabine Salvucci 2E]

Hello! I think K and Kc are basically the same thing, both representing the equilibrium constant, but Kc is more specific. K can refer to concentration, pressure, etc., while Kc specifically refers to concentration. Hope this helps!

[Sam_Marasigan_3D]

I believe K is just the equilibrium constant. We differentiate it by using Kc or Kp.

[Margaret Wang 2D]

K is a broad term for the equilibrium constant. Kc and Kp are more specific versions of the equilibrium constant, although most of the time K means Kc (from my observations)

[Alara Aygen 3K]

They are used interchangeably.

[My-Lan Le 1L]

Like what all of the other posts say, they can be used interchangeably and basically are the same thing, but K is more general and Kc is referring to the concentrations. The c subscript is used to specify that the concentration is being used. I think in the next lectures, Dr. Lavelle will talk about other subscripts like p which refers to pressure.

[Violet Kwan 3H]

I also agree with the posts above. Since the difference between the two is small, they can basically be considered the same or used interchangeably. Just depends on which specific concentration you need or what the question calls for.

[Jack_Pearce_2H]

Kc usually deals with equilibrium regarding concentrations and K is a more general term for the eq. constant. Hope this helps!

[Adam Bustamante 1I]

K is an equilibrium constant, but Kc is understood as an equilibrium of concentration constant, so they're basically the same. K is just a broader term.

[Crystal Pan 2G]

K is the equilibrium constant and can be Kp or Kc. Kc is used for concentrations.

[Nicolette Simoni 3L]

I agree with the statements above but one thing to also keep in mind is that when calculating the equilibrium constant from thermodynamic tables of data (the standard gibbs free energy for example), you have to give K, not Kc.

[Megan Hulsy 1A]

K is the generalized term for the equilibrium constant. Kc is just a specific format for concentrations! :)

[Anna Yang 1A]

K means equilibrium constant. Kc denotes its specification for concentrations while Kp denotes its specification for gases/pressure.

[Annika Tamaki 1E]

K just represents concentration, whereas Kc represents the constant equilibrium concentration.