## when to use Kc vs Kp

Sarah Blake-2I
Posts: 153
Joined: Fri Aug 30, 2019 12:16 am

### when to use Kc vs Kp

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
Posts: 103
Joined: Sat Aug 17, 2019 12:17 am
Been upvoted: 1 time

### Re: when to use Kc vs Kp

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
Posts: 106
Joined: Fri Aug 09, 2019 12:16 am

### Re: when to use Kc vs Kp

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
Posts: 107
Joined: Wed Sep 18, 2019 12:16 am

### Re: when to use Kc vs Kp

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
Posts: 100
Joined: Sat Aug 17, 2019 12:17 am

### Re: when to use Kc vs Kp

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
Posts: 66
Joined: Sat Aug 17, 2019 12:16 am

### Re: when to use Kc vs Kp

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
Posts: 100
Joined: Thu Jul 25, 2019 12:15 am

### Re: when to use Kc vs Kp

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

AronCainBayot2K
Posts: 101
Joined: Fri Aug 30, 2019 12:17 am

### Re: when to use Kc vs Kp

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
Posts: 107
Joined: Fri Aug 02, 2019 12:15 am

### Re: when to use Kc vs Kp

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
Posts: 94
Joined: Wed Sep 18, 2019 12:18 am

### Re: when to use Kc vs Kp

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
Posts: 97
Joined: Sat Aug 24, 2019 12:17 am

### Re: when to use Kc vs Kp

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

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.