when to use Kc vs Kp

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Sarah Blake-2I
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Joined: Fri Aug 30, 2019 12:16 am

when to use Kc vs Kp

Postby Sarah Blake-2I » Sun Jan 12, 2020 10:37 am

When writing out the Kc or Kp, how do we know when to show the values in brackets (concentration) vs using P and a subscript of the element. What I am trying to ask is do we only write the values in brackets if we are calculating Kc?

KeyaV1C
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Re: when to use Kc vs Kp

Postby KeyaV1C » Sun Jan 12, 2020 10:47 am

The sure brackets around the compound just indicate that you’re writing the concentration of the compound => [] = concentration. You use p to calculate kp only when the compounds in the reaction are gases.

Jamie Lee 1F
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Re: when to use Kc vs Kp

Postby Jamie Lee 1F » Sun Jan 12, 2020 11:28 am

Kc is defined by molar concentrations, while Kp is defined by partial pressures of gases. You typically use brackets for K and Kc, and parentheses for Kp.

Jared Khoo 1G
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Re: when to use Kc vs Kp

Postby Jared Khoo 1G » Sun Jan 12, 2020 11:44 am

By using brackets you are denoting a value that is concentration, therefore you should plug in concentrations with the units molL-1, which will get you Kc.

Matt F
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Re: when to use Kc vs Kp

Postby Matt F » Sun Jan 12, 2020 12:06 pm

As others mentioned, brackets denote concentration (in mol.L-1), so you wouldn't use them when calculating partial pressure for Kp. However, just because you are given all gases does not necessarily mean you will be calculating Kp, so pay attention to what the question asks and what values are given

IScarvie 1E
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Re: when to use Kc vs Kp

Postby IScarvie 1E » Sun Jan 12, 2020 12:45 pm

The brackets are strictly used to show that we are dealing with molar concentrations, and are used to solve for kc. Parenthesis and kp are used to deal with pressure

Maya Gollamudi 1G
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Re: when to use Kc vs Kp

Postby Maya Gollamudi 1G » Sun Jan 12, 2020 1:02 pm

The brackets indicate that the number inside is a concentration (molarity). Parentheses mean that the number is a partial pressure of a gas.

AronCainBayot2K
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Re: when to use Kc vs Kp

Postby AronCainBayot2K » Sun Jan 12, 2020 1:17 pm

Kc usually deals with molar concentration and the activity of chemical reactions. Kp deals with partial pressure only when the products and reactants are forms of gasses.

Betania Hernandez 2E
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Re: when to use Kc vs Kp

Postby Betania Hernandez 2E » Sun Jan 12, 2020 2:35 pm

Kc uses brackets because it is dealing with the molar concentration while it isn't used with Kp because it is dealing with gases which is in the units of bar or atm.

JohannaPerezH2F
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Re: when to use Kc vs Kp

Postby JohannaPerezH2F » Sun Jan 12, 2020 2:50 pm

we use Kc or Kp according to the the information we are given and the values we are looking for. for example we would use Kp when atm is used and Kc when moles/liter are used

Helen Struble 2F
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Re: when to use Kc vs Kp

Postby Helen Struble 2F » Sun Jan 12, 2020 3:10 pm

Matt F wrote:As others mentioned, brackets denote concentration (in mol.L-1), so you wouldn't use them when calculating partial pressure for Kp. However, just because you are given all gases does not necessarily mean you will be calculating Kp, so pay attention to what the question asks and what values are given


Brackets do denote concentration, but it's important to note that because concentration is used as an approximation for chemical activity, the typical units for concentration are omitted when calculating Kc.

005324438
Posts: 51
Joined: Sat Aug 24, 2019 12:16 am

Re: when to use Kc vs Kp

Postby 005324438 » Sun Jan 12, 2020 4:35 pm

The brackets represent molarity, and the P represents partial pressure. The only time to use P is when we are dealing with gasses, it should be (g) as a subscript in the chemical equation this calculates Kp. If it has an (aq) it is a solution with a concentration, and we can use the bracket, this calculates Kc.


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