## Kc vs Kp

$PV=nRT$

connie 2C
Posts: 106
Joined: Thu Jul 11, 2019 12:17 am

### Kc vs Kp

when a chemical equation is written and all the reactants and products are gases, do you use Kp rather than Kc? in what cases do you use Kc rather than Kp?

ayushibanerjee06
Posts: 177
Joined: Thu Jul 11, 2019 12:16 am
Been upvoted: 1 time

### Re: Kc vs Kp

You use Kp when all the products and reactants are gases and the question includes units like bar/atm/pa. You use Kc when the products and reactants are given in moles or molarity, even if the products and reactants are gases. If the question asks for Kp and the question only gives you information about moles/molarity, use the ideal gas law and solve for pressure (P= (n/v)RT). Vice versa if they ask for Kc and they only give you information about pressure. Also, keep in mind there are different gas constants, so use the one that fits the units you have. Hope this helps.

Rida Ismail 2E
Posts: 139
Joined: Sat Sep 07, 2019 12:16 am

### Re: Kc vs Kp

Kc is used when you have the molarity of a solution. Kp is always used with gases.

Justin Quan 4I
Posts: 104
Joined: Sat Sep 14, 2019 12:17 am

### Re: Kc vs Kp

To add on, you use Kp when the reactants and products are gases. If your reaction has gases and/or aqueous substances, then use Kc. However, if you're still having trouble deciding, you should check the units to ensure you're using the right K, for example Barr (pressure) vs M (concentration).

Minh Ngo 4G
Posts: 137
Joined: Thu Jul 25, 2019 12:17 am

### Re: Kc vs Kp

If all the reactants are gas then use Kp. You can calculate Kc for gas too but they would have to explicitly tell you so

Ying Yan 1F
Posts: 101
Joined: Fri Aug 02, 2019 12:16 am

### Re: Kc vs Kp

It really depends what information the problems gives you. If the concentrations of the reactants and products are given, then you you Kc, on the other hand, if the pressure of the reactants and products are given then you use Kp.

ValerieChavarin 4F
Posts: 99
Joined: Wed Sep 18, 2019 12:18 am

### Re: Kc vs Kp

It depends on what asked and given. If you are calculating molar concentration then you would use Kc.

805373590
Posts: 101
Joined: Wed Sep 11, 2019 12:17 am

### Re: Kc vs Kp

You can use kp when the reactants and products are gases and the partial pressures of the gases are given rather than their concentrations

vanessas0123
Posts: 100
Joined: Wed Sep 11, 2019 12:17 am

### Re: Kc vs Kp

You calculate Kc if given concentration. Kp if partial pressures are given.

Posts: 50
Joined: Tue Nov 05, 2019 12:18 am

### Re: Kc vs Kp

You use Kc when you are given a concentration, while Kp is used when given partial pressures. However, you can use Kp to find Kc if needed.

Angela Prince 1J
Posts: 102
Joined: Sat Aug 24, 2019 12:17 am

### Re: Kc vs Kp

connie 2C wrote:when a chemical equation is written and all the reactants and products are gases, do you use Kp rather than Kc? in what cases do you use Kc rather than Kp?

You can use whatever is convenient when they're all gases. You cannot use KP if it's not a gas.

Zoe Gleason 4F
Posts: 51
Joined: Tue Jul 23, 2019 12:15 am

### Re: Kc vs Kp

Kp can be used when all the concentrations are in pressure, and Kc when they are concentrations. Pressure can be converted to concentration by using PV=nRT (and vice versa), but all the species must be in the gas phase to use Kp.

Leila_4G
Posts: 114
Joined: Sat Sep 14, 2019 12:17 am

### Re: Kc vs Kp

From what I understand, pressures can be used with Kc or Kp but concentrations can only be used with Kc. Right?

Gurmukhi Bevli 4G
Posts: 49
Joined: Wed Nov 14, 2018 12:20 am

### Re: Kc vs Kp

Kc is used when you're dealing with molar concentrations, or when all the substances in your reaction are aqueous. Kp is used for partial pressures, or when the substances in your reaction are all gases.

annikaying
Posts: 94
Joined: Sat Sep 14, 2019 12:16 am

### Re: Kc vs Kp

kp is used when dealing with gases and is usually given with units like atm or bar. kc is for molar concentrations and will be given as aqueous solutions.

905373636
Posts: 62
Joined: Thu Aug 01, 2019 12:15 am

### Re: Kc vs Kp

The difference here just has to do with units used, though Kp will include all gases yes.

WYacob_2C
Posts: 102
Joined: Sat Jul 20, 2019 12:16 am

### Re: Kc vs Kp

Kp is used when dealing with partial pressures, so typically gases. Kc is used when dealing with concentration, so aqueous species.

Emil Velasco 1H
Posts: 96
Joined: Wed Nov 21, 2018 12:19 am

### Re: Kc vs Kp

You use Kp unless it specifically asks for Kc

William Francis 2E
Posts: 101
Joined: Wed Sep 18, 2019 12:20 am

### Re: Kc vs Kp

Kp should be used with gases since you're dealing with partial pressures rather than concentrations.

Tahlia Mullins
Posts: 105
Joined: Thu Jul 25, 2019 12:15 am

### Re: Kc vs Kp

It all depends on the information given. You would use Kp when the partial pressures are given, but you use Kc when the concentration or moles or grams are given even when the reactants and products are gases.

Kylie Lim 4G
Posts: 110
Joined: Sat Aug 17, 2019 12:15 am

### Re: Kc vs Kp

For a reaction that is entirely gasses, Kp can be used if the pressure is given. Kc can be used for gasses as well if the pressure is converted to concentration, or concentration is given initially.

Megan Cao 1I
Posts: 103
Joined: Sat Sep 07, 2019 12:18 am

### Re: Kc vs Kp

kp is used for gases since they deal with Pressure. kc is used for questions involving molarity, generally solutions, however you can find the concentration of gases too. you would have to use the ideal gas law, pv=nrt

Caroline Zepecki
Posts: 101
Joined: Fri Aug 09, 2019 12:16 am

### Re: Kc vs Kp

Kp is for partial pressures of gasses, Kc on the other hand is the equilibrium constants

Hannah Pham
Posts: 104
Joined: Fri Aug 09, 2019 12:17 am

### Re: Kc vs Kp

If the reaction consists of all gases then you would use Kp. Kc can be used for gases as well if the gases are given in concentration rather than pressure.

105311039
Posts: 107
Joined: Fri Aug 02, 2019 12:16 am

### Re: Kc vs Kp

Kp is used with partial pressures like gases such as ATM. But Kc is used when you have things like aq concentrations.

Anushka Chauhan2B
Posts: 51
Joined: Sat Aug 24, 2019 12:16 am

### Re: Kc vs Kp

Kp should be used for gases since you are dealing with partial pressures

Jesse Anderson-Ramirez 3I
Posts: 54
Joined: Thu Sep 26, 2019 12:18 am

### Re: Kc vs Kp

Kp is for gases and uses partial pressure. Kc uses concentrations.

Astrid Lunde 1I
Posts: 103
Joined: Sat Sep 07, 2019 12:16 am

### Re: Kc vs Kp

Kp is when you deal with partial pressure so it is used for gasses. Use Kc when you see aq.

KaleenaJezycki_1I
Posts: 127
Joined: Sat Aug 17, 2019 12:18 am
Been upvoted: 2 times

### Re: Kc vs Kp

connie 2C wrote:when a chemical equation is written and all the reactants and products are gases, do you use Kp rather than Kc? in what cases do you use Kc rather than Kp?

Kc should be used normally, but the question will clarify if it wants molar concentrations or partial pressures. Therefore pay attention to the question, also Kc will be in units of mol.L-1 and Kp will be in bar or atm.

205405339
Posts: 77
Joined: Thu Jul 11, 2019 12:16 am

### Re: Kc vs Kp

You use Kp because K=kp for all cases. Kc=K when certain conditions are met

MTanikella_1K
Posts: 110
Joined: Sat Jul 20, 2019 12:16 am

### Re: Kc vs Kp

Kp is used when all products and reactants in the equation are gases. Another indication to use Kp is if the question uses units like bar or atm. Kc is used when the molarity of the products and reactants is given, even though the products and reactants involved in the reaction are gases.

Aarushi Solanki 4F
Posts: 107
Joined: Sat Jul 20, 2019 12:17 am

### Re: Kc vs Kp

Kp is used when the quantity of gases are given in context of pressure. Kc is used when the molarity of solutions or gases are given.

Rosa Munoz 2E
Posts: 105
Joined: Wed Sep 18, 2019 12:21 am

### Re: Kc vs Kp

Kc is concentration Kp is partial pressure.

Hannah Romeo 1J
Posts: 58
Joined: Thu Jul 11, 2019 12:16 am

### Re: Kc vs Kp

You use Kc when you have concentrations in molarity snd use Kp when you have partial pressures.

Maika Ngoie 1B
Posts: 97
Joined: Fri Aug 02, 2019 12:16 am

### Re: Kc vs Kp

In that instance, you would use Kp, Kc is used for molar concentration.

William Chan 1D
Posts: 102
Joined: Sat Sep 14, 2019 12:15 am

### Re: Kc vs Kp

If the reactants and products are given in units of pressure (bars, atmospheres, etc.), then use kp. If reactants and products are given in units of concentration (mol/L), then use kc.

Jasmine W 1K
Posts: 49
Joined: Sat Sep 07, 2019 12:18 am

### Re: Kc vs Kp

Kp is used with gases and Kc is used when you are dealing with concentrations.

Ryan Yoon 1L
Posts: 55
Joined: Mon Jul 01, 2019 12:15 am

### Re: Kc vs Kp

Kc deals with concentrations and Kp deals with atm and torr.

Alan Cornejo 1a
Posts: 98
Joined: Fri Aug 30, 2019 12:15 am

### Re: Kc vs Kp

Kp is used in the event that you products and reactants all exists in a gas phase. Therefore we use the partial pressures of the gases and make sure the units we use as a result also take that into inclusion. For Kc we use that when we are trying to determine concentration rather than the pressure.

Bryce Barbee
Posts: 103
Joined: Wed Sep 18, 2019 12:20 am

### Re: Kc vs Kp

It depends on if the give you pressures or concentrations. I am pretty sure that you can use both if its a gas though.

Catherine Daye 1L
Posts: 104
Joined: Wed Sep 11, 2019 12:16 am

### Re: Kc vs Kp

You use Kp for gases if you use partial pressure for gases. You can also change pressure to concentration using PV=nRT and in that case, you would use Kc since you’re now using concentrations.

Gerald Bernal1I
Posts: 102
Joined: Thu Jul 11, 2019 12:16 am

### Re: Kc vs Kp

Kc is used if you are given concentrations and Kp is used when you are given partial pressures.

805422680
Posts: 103
Joined: Sat Sep 14, 2019 12:16 am

### Re: Kc vs Kp

Kc is used when you are given concentrations, and Kp is used when you are given partial pressures of gases. When Kp is given, the products and reactants are both gases. When Kc is given, the products and reactants can consist of gases or aqueous solutions

briannam_1F
Posts: 35
Joined: Wed Sep 18, 2019 12:18 am

### Re: Kc vs Kp

Kc is used when molarity is given. When it comes to gas you only use Kp when given partial pressures or asked to convert to partial pressures.

austin-3b
Posts: 67
Joined: Wed Nov 11, 2020 12:18 am

### Re: Kc vs Kp

You use Kc when having the molar concentrations of the particles and Kp for when given the pressures (I think only gases have kp values).

Crystal Pan 2G
Posts: 118
Joined: Wed Sep 30, 2020 10:04 pm
Been upvoted: 2 times

### Re: Kc vs Kp

Depends on what the problem gives you. If it gives you units in bar/atm, it will most likely be Kp. If it gives you units in M or x moles in x L, it will probably be Kc.

Andy Hon 3E
Posts: 49
Joined: Wed Nov 18, 2020 12:27 am

### Re: Kc vs Kp

Kc should be used when questions give the concentration in mol/liter and Kp is for partial pressure. However, there is an equation to convert between the two if need be.

SavannahScriven_1F
Posts: 98
Joined: Wed Sep 30, 2020 9:37 pm

### Re: Kc vs Kp

If given a chemical equation and some of the reactants and products are in a solution (designated by aq), then you must use Kc. This makes sense as you are dealing with solutions and in a lab setting, concentration is important to know. (you wouldn't randomly measure/convert the reagents to P). If given a chemical equation and all the reactants/products inputted into the K equation are gases, then it is standard to use partial pressure. In a lab, it's more natural to find the pressure of a gas rather than its concentration.

Simi Kapila_3E
Posts: 95
Joined: Wed Sep 30, 2020 9:40 pm
Been upvoted: 1 time

### Re: Kc vs Kp

Use Kp when all products and reactants are in the gas phase, and you Kc in any other circumstance. But remember, you never include solids and liquids when determining the equilibrium constant, only molecules in aqueous or gaseous form.

Jordan Tatang 3L
Posts: 120
Joined: Wed Sep 30, 2020 9:31 pm
Been upvoted: 3 times

### Re: Kc vs Kp

yeah as all the others said you would use Kc for concentration and Kp for pressure

Jordi M 2I
Posts: 144
Joined: Wed Sep 30, 2020 9:40 pm

### Re: Kc vs Kp

It depends on what the question gives you and what it is asking for. If it gives you the concentration of a reactant or product, use Kc. If it gives you a pressure, use Kp.

Funmi Baruwa
Posts: 108
Joined: Wed Sep 30, 2020 9:50 pm

### Re: Kc vs Kp

when the reactants and products use Kp which is for partial pressure and use Kc when the reactants or products are in aqueous form. when the reactants or products are solids or liquids we disregard them.

hope this helps!! :)

Yeonjoo Kim 2B
Posts: 14
Joined: Wed Sep 18, 2019 12:17 am

### Re: Kc vs Kp

Kc is an equilibrium constant for gases and is found through the use of partial pressure; Kp is an equilibrium constant which is found through the use of concentrations

Kelly Ha 1K
Posts: 93
Joined: Wed Sep 30, 2020 9:52 pm
Been upvoted: 1 time

### Re: Kc vs Kp

Kc is used for concentrations while Kp is used for pressures. If you are given the concentrations of reactants and products, use Kc. If you are given partial pressures of reactants and products, use Kp. It's also important to note that you should use Kp if all products and reactants in the reaction are in the gas phase.

Kelly Ha 1K
Posts: 93
Joined: Wed Sep 30, 2020 9:52 pm
Been upvoted: 1 time

### Re: Kc vs Kp

Yeonjoo Kim 2B wrote:Kc is an equilibrium constant for gases and is found through the use of partial pressure; Kp is an equilibrium constant which is found through the use of concentrations

Someone correct me if I am wrong, but I believe it is switched! Kp is the equilibrium constant used for when all products and reactants are gases while Kc is related to concentration and is used for reactions that have products and reactants in aqueous phases.

Kaley Qin 1F
Posts: 96
Joined: Wed Sep 30, 2020 9:54 pm

### Re: Kc vs Kp

If the problem gives partial pressures of reactants or products or it asks for the partial pressures, use Kp. Otherwise use Kc. Also in lecture, Lavelle talks about the way to get the conc of a gas from knowing its partial pressure. So if need be you could do that.

Anusha Chaudhary 1J
Posts: 41
Joined: Thu Dec 17, 2020 12:18 am

### Re: Kc vs Kp

Kelly Ha 1K wrote:
Yeonjoo Kim 2B wrote:Kc is an equilibrium constant for gases and is found through the use of partial pressure; Kp is an equilibrium constant which is found through the use of concentrations

Someone correct me if I am wrong, but I believe it is switched! Kp is the equilibrium constant used for when all products and reactants are gases while Kc is related to concentration and is used for reactions that have products and reactants in aqueous phases.

I agree. Kc is for equilibrium constant found from concentrations, while Kp is the equilibrium constant found using the partial pressures.

Lily Anne Garcia 1C
Posts: 88
Joined: Wed Sep 30, 2020 9:55 pm

### Re: Kc vs Kp

Kc refers to concentration while Kp refers to pressure. You calculate either or depending on what values you were given in the problem.

John_Tran_3J
Posts: 97
Joined: Wed Sep 30, 2020 9:58 pm

### Re: Kc vs Kp

I agree with the post above regarding the use of Kp with gases and Kc with concentration. You can also make note if you were given the concentration whether if it's in MOLS (Kc) or BARS (Kp).

lwon Dis2I
Posts: 104
Joined: Wed Sep 30, 2020 9:37 pm

### Re: Kc vs Kp

You use Kp when you are dealing with gases, but use Kc when you are dealing with molarity.

Victoria Dao 3G
Posts: 99
Joined: Wed Sep 30, 2020 9:50 pm

### Re: Kc vs Kp

Hi! I was also confused by this initially because in AP chem we brushed over this concept pretty quickly. But the difference is mainly that Kp deals with partial pressures of gases while Kc is in consideration of the concentrations of gases. Both are equilibrium constants of gas though.

Gigi Elizarraras 2C
Posts: 95
Joined: Wed Sep 30, 2020 9:41 pm

### Re: Kc vs Kp

To me Kc makes the most sense so I would tend to use it, but when a problem dealing with gases explicitly gives you partial pressures(atm) us Kp:)

Brianna Chen 3F
Posts: 103
Joined: Wed Sep 30, 2020 10:11 pm

### Re: Kc vs Kp

Like others have said above, it depends on the problem given. Sometimes, an equation would only contain gases, yet they would calculate Kc. Typically, the problem would hint whether they want you to solve for Kc or Kp based on the units given.

Jason_John_2F
Posts: 91
Joined: Wed Sep 30, 2020 9:54 pm

### Re: Kc vs Kp

kp is used if it is calculated using partial pressure while kc is used if it is calculated using concentration

Krish_Ajmani_3J
Posts: 16
Joined: Wed Nov 20, 2019 12:20 am

### Re: Kc vs Kp

Leila_4G wrote:From what I understand, pressures can be used with Kc or Kp but concentrations can only be used with Kc. Right?

Yes that's right. Pressures can be used with either Kc or Kp and is dependent on the information provided in the problem. Concentrations can only be used with Kc and the concentrations required to solve the problem will be given.

Chudi Onyedika 3A
Posts: 94
Joined: Wed Sep 30, 2020 9:37 pm

### Re: Kc vs Kp

If you are using concentrations, then use Kc. If you are using pressures, then use Kp.

Sophia Spungin 2E
Posts: 98
Joined: Wed Sep 30, 2020 9:41 pm

### Re: Kc vs Kp

The version of K used is dependent on how the value of K is calculated. If you used concentration of products and reactants to calculate K, then use Kc to denote this. If you used partial pressures to calculate K, them use Kp.

Melis Kasaba 2B
Posts: 91
Joined: Wed Sep 30, 2020 9:49 pm

### Re: Kc vs Kp

Kc and Kp are both equilibrium constants for mixtures of gases, but Kc depends on molar concentrations whereas Kp depends on the partial pressures of gasses inside a closed system.

Sean Wang 1F
Posts: 95
Joined: Wed Sep 30, 2020 9:34 pm

### Re: Kc vs Kp

Kc is used for concetrations while Kp is used for partial pressurse.

Jason Knight - 1F
Posts: 107
Joined: Wed Sep 30, 2020 9:55 pm

### Re: Kc vs Kp

After reviewing the question you will have a better sense if Kc or Kp is being used. By definition, Kc is used when working with concentrations and Kp is used when working with partial pressure. It is important to note that Kp only applies to reactions with all (R) and (P) molecules in the gas phase.

Ava Nickman
Posts: 100
Joined: Wed Sep 30, 2020 9:54 pm

### Re: Kc vs Kp

If the question does not specifically indicate which K is wants, look at the units given. If they are pressure units like bar, you are finding Kp... if not, find Kc

Simer_Shera_2D
Posts: 110
Joined: Wed Sep 30, 2020 9:58 pm
Been upvoted: 1 time

### Re: Kc vs Kp

From my understanding, Kp is when all the products and reactants are gases. If the reaction is heterogenous, then you would use Kc.

Kayla Booker 1F
Posts: 90
Joined: Wed Sep 30, 2020 9:43 pm

### Re: Kc vs Kp

You would use Kp.

Dominic Benna 2E
Posts: 98
Joined: Wed Sep 30, 2020 10:09 pm

### Re: Kc vs Kp

Kc is always used when you are given the molar concentrations or the moles of the products or reactants. Kp is used when you have only gases, or if, in the equation, it mentions atm/bar for the units.

Posts: 113
Joined: Wed Sep 30, 2020 9:51 pm

### Re: Kc vs Kp

Kc is for molarity
Kp is more atms/bars

Karen Elrayes 1L
Posts: 92
Joined: Wed Sep 30, 2020 9:45 pm

### Re: Kc vs Kp

if they are all gases, you would most likely use Kp because gases aren't usually given in concentration. It also depends on the units you are given, so if you are given a value in concentration, you can convert everything to mol/l using the ideal gas equation PV=nRT

Carlos Martinez 2K
Posts: 15
Joined: Wed Nov 14, 2018 12:20 am

### Re: Kc vs Kp

Kc and Kp are the equilibrium constants of gaseous mixtures. However, the difference between the two constants is that Kc is found by obtaining by molar concentrations, whereas Kp is defined by obtaining the partial pressures of the gasses inside a closed system.

Kathy_Li_1H
Posts: 90
Joined: Wed Sep 30, 2020 9:31 pm

### Re: Kc vs Kp

Hi! The difference is that you use Kc with concentrations/aqueous mixtures and Kp is used for pressure/ gases.

Hana Sigsbee 3B
Posts: 97
Joined: Wed Sep 30, 2020 10:00 pm

### Re: Kc vs Kp

The c in Kc refers to concentration and the p in Kp refers to pressure so for equations referring to gases you would use Kp as it refers to the pressure of the gas.

Emma_Barrall_3J
Posts: 95
Joined: Wed Sep 30, 2020 9:55 pm

### Re: Kc vs Kp

Kp is for homogeneous gaseous reactions. Otherwise you Kc. According to UA session: he will specify whether to use Kp or Kc when both are applicable.

Alison Perkins 2B
Posts: 95
Joined: Wed Sep 30, 2020 9:57 pm
Been upvoted: 1 time

### Re: Kc vs Kp

When the problem contains all gases, you can use Kp if the pressure measurements are given. If you are given measurements for concentration rather than pressure, however, it is okay to use Kc.

alexandralopez 3F
Posts: 92
Joined: Wed Sep 30, 2020 10:11 pm

### Re: Kc vs Kp

You only use Kp for gases/calculating partial pressure

Edwin Liang 1I
Posts: 93
Joined: Wed Sep 30, 2020 9:34 pm

### Re: Kc vs Kp

Kc is used for problems with molarity and Kp for calculating pressures of gas.

Halle Villalobos 3E
Posts: 90
Joined: Wed Sep 30, 2020 9:52 pm

### Re: Kc vs Kp

Hi! It really depends on what units are given to you and the context of the problem. But generally speaking, you would use Kp when working with gases because they are the only ones that have partial pressures. If you need to convert, use the ideal gas law (PV = nRT) to determine the concentration when given atm/bar/pa or to determine pressure when given something in moles or molarity. I hope this helps!

Eric Ngo 1F
Posts: 40
Joined: Tue Nov 17, 2020 12:18 am

### Re: Kc vs Kp

I believe Kp is used for gasses, but if conversion is necessary using PV = nRT is really helpful! n/V being concentration.

LeanneBagood_2F
Posts: 96
Joined: Wed Sep 30, 2020 9:32 pm

### Re: Kc vs Kp

like others have previously said, the way you can tell if you use Kc or Kp is by looking at the units you are given in the equation. Kc is when you use mols whereas Kp is when you see atms/bars

Mingzi Yang 1E
Posts: 90
Joined: Wed Sep 30, 2020 9:53 pm

### Re: Kc vs Kp

You use Kp when all the reactants and products are gases. If the reactants and products are given in molar concentration, then you should use Kc.

Taha 2D
Posts: 80
Joined: Wed Sep 30, 2020 9:50 pm

### Re: Kc vs Kp

if everything (rectants/products) are in gaseous states then KP is used, otherwise KC

AlbertGu_2C
Posts: 91
Joined: Wed Sep 30, 2020 9:34 pm

### Re: Kc vs Kp

You would use Kc if the moles are given, and if the partial pressures are given, use Kp. If both are given then you would have to use the Ideal Gas Law along with given information to convert between the two. Hope this helps!

rhettfarmer-3H
Posts: 101
Joined: Wed Sep 30, 2020 9:59 pm

### Re: Kc vs Kp

Well to begin it has to be said that Kc refers to concentration and Kp is referring to pressure. With that, the first note is that Kp sorely can be used for gases. Whereas, Kc can be used universally. so one asks when do you pick which one? Well, remember it is based on the equation states and what you are given. If they give pressure such barr or atm and all are gases then it makes sense that you are going to be finding Kp. If you are given molarity well then it makes sense you will be finding concentration and be looking for Kc.

Tobie Jessup 2E
Posts: 89
Joined: Wed Sep 30, 2020 10:02 pm

### Re: Kc vs Kp

ayushibanerjee06 wrote:You use Kp when all the products and reactants are gases and the question includes units like bar/atm/pa. You use Kc when the products and reactants are given in moles or molarity, even if the products and reactants are gases. If the question asks for Kp and the question only gives you information about moles/molarity, use the ideal gas law and solve for pressure (P= (n/v)RT). Vice versa if they ask for Kc and they only give you information about pressure. Also, keep in mind there are different gas constants, so use the one that fits the units you have. Hope this helps.

This was very helpful thank you!

joshtully
Posts: 92
Joined: Wed Sep 30, 2020 9:36 pm

### Re: Kc vs Kp

Kc is used when given concentration, and Kp is used when given partial pressures.

Shivani Kapur 2J
Posts: 100
Joined: Wed Sep 30, 2020 9:59 pm

### Re: Kc vs Kp

Kp should be used when dealing with gases. Hope this helps!

Keshav Patel 14B 2B
Posts: 94
Joined: Wed Sep 30, 2020 9:40 pm

### Re: Kc vs Kp

Use KP when you have anything to do with pressure. If you see any given partial pressure you want to use KP while KC is for varying molarity/ amount of the product/reactants you have.

Melanie Lin 3E
Posts: 90
Joined: Wed Sep 30, 2020 9:38 pm

### Re: Kc vs Kp

Kp is used when the reactants and products are in gaseous form (make sure they're all in the same units before you input into the formula!). Kc is used usually when the reaction occurs in solution, so you use the concentrations of aqueous reactants and products. Be sure not to include liquid or solids in the equation! Hope this helps!

Hannah Lechtzin 1K
Posts: 94
Joined: Wed Sep 30, 2020 9:31 pm

### Re: Kc vs Kp

Kp just indicated that you used partial pressures (gases) in your equilibrium equation, while Kc indicated that you used concentrations in the equilibrium equation.

Diana Aguilar 3H
Posts: 90
Joined: Wed Sep 30, 2020 9:50 pm

### Re: Kc vs Kp

Thank you to everyone for the explanations, I was also having trouble with this!

Samir 3I
Posts: 43
Joined: Wed Sep 30, 2020 10:04 pm

### Re: Kc vs Kp

One thing I wasn't completely clear on is when we calculate Kc our notation for setting up the equation should use the brackets to denote concentration but when we calculate Kp we use "P" to denote partial pressure?

Zihan Liu 2K
Posts: 15
Joined: Tue Jan 14, 2020 12:15 am

### Re: Kc vs Kp

You use Kc when the concentrations of reactants and products are given, and you use Kp when partial pressures are given

Rachel Kho Disc 2G
Posts: 79
Joined: Wed Sep 30, 2020 9:46 pm

### Re: Kc vs Kp

Also will we need to have the formula that converts Kc to Kp memorized? Or will that be given to us on an equations sheet?