Kc and Kp


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Ghadir Seder 1G
Posts: 134
Joined: Sat Sep 14, 2019 12:17 am

Kc and Kp

Postby Ghadir Seder 1G » Mon Jan 13, 2020 4:06 pm

Why and how are Kc and Kp calculated the same way but represent different values?

McKenna_4A
Posts: 115
Joined: Sat Aug 24, 2019 12:18 am

Re: Kc and Kp

Postby McKenna_4A » Mon Jan 13, 2020 4:07 pm

One is measuring based on concentration and the other by pressure. They both represent the same thing because they are simply a ration between chemical compounds, not values with units.

Charisse Vu 1H
Posts: 101
Joined: Thu Jul 25, 2019 12:17 am

Re: Kc and Kp

Postby Charisse Vu 1H » Mon Jan 13, 2020 4:12 pm

Kc and Kp both measure the equilibrium constant of a reaction. Kc is used when calculating in terms of concentration whereas Kp is used when calculating in terms of pressure. Typically, you would calculate the Kp of a reaction that is made up of all gases, but both Kp and Kc should be the same since they are simply ratios.

Jordan Ziegler 2J
Posts: 59
Joined: Sat Aug 17, 2019 12:15 am

Re: Kc and Kp

Postby Jordan Ziegler 2J » Mon Jan 13, 2020 5:21 pm

I understand your confusion; in the textbook, Kc and K are assigned different values in some parts of Table 5G.2. However, this isn't something to worry about, since because when there was ambiguity involved with which values to use, the question provided the correct constant. I expect the same will carry over for exam questions.

Like everyone above said, Kc represents the equilibrium constant found using concentrations of products and reactants. The values of K and Kc are only different in the textbook when it's a gas reaction. All in all, careful reading is a good takeaway.

Tiffany_Chen 2K
Posts: 106
Joined: Fri Aug 30, 2019 12:15 am

Re: Kc and Kp

Postby Tiffany_Chen 2K » Mon Jan 13, 2020 5:21 pm

The question should indicate which one to use. Though all reactants/products can be in gas form, we can still look and compare their concentrations (Kc).

Esha Chawla 2E
Posts: 108
Joined: Thu Jul 25, 2019 12:17 am

Re: Kc and Kp

Postby Esha Chawla 2E » Mon Jan 13, 2020 5:28 pm

Ghadir Seder 1G wrote:Why and how are Kc and Kp calculated the same way but represent different values?


Kc is calculated using concentrations. Kp is calculated using pressure. Because the constants are calculated using different values, the values of Kc and Kp, the constants are also going to be different.


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