When to use K and Kp

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Bilal Pandit 1J
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Joined: Wed Sep 11, 2019 12:16 am

When to use K and Kp

Postby Bilal Pandit 1J » Wed Jan 15, 2020 5:38 pm

When you are given a random chemical equation, does it matter if you use K or Kp (concentration or pressure) if the question doesn't specifically state what it wants?

Hiba Alnajjar_2C
Posts: 108
Joined: Fri Aug 09, 2019 12:17 am

Re: When to use K and Kp

Postby Hiba Alnajjar_2C » Wed Jan 15, 2020 5:39 pm

If it doesn't specify Kc or Kp, either should be fine. However, you should be able to tell what the question wants based on what's given. For example, if it gives you concentration values, you would probably have to find Kc.

Subashni Rajiv 1K
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Re: When to use K and Kp

Postby Subashni Rajiv 1K » Wed Jan 15, 2020 6:08 pm

Typically, if the problem gives concentration, then Kc is used. In most cases, it will be easy to know what you are asked for, if not specified.

Kristina Rizo 2K
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Re: When to use K and Kp

Postby Kristina Rizo 2K » Wed Jan 15, 2020 6:52 pm

I thought Kp was used for gas only? Can someone clarify this please.

Kallista McCarty 1C
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Joined: Wed Sep 18, 2019 12:18 am

Re: When to use K and Kp

Postby Kallista McCarty 1C » Wed Jan 15, 2020 8:20 pm

Kristina Rizo 2K wrote:I thought Kp was used for gas only? Can someone clarify this please.

Kp is used for gases to determine partial pressures! Kc is used for concentrations and Ka and Kb are for acids and bases.

Maya Pakulski 1D
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Joined: Thu Jul 11, 2019 12:17 am

Re: When to use K and Kp

Postby Maya Pakulski 1D » Wed Jan 15, 2020 8:34 pm

Kallista McCarty 1C wrote:
Kristina Rizo 2K wrote:I thought Kp was used for gas only? Can someone clarify this please.

Kp is used for gases to determine partial pressures! Kc is used for concentrations and Ka and Kb are for acids and bases.


This might be a dumb question but you calculate all of these the same way right, with products/reactants?

Lizette Noriega 1H
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Joined: Wed Sep 18, 2019 12:15 am

Re: When to use K and Kp

Postby Lizette Noriega 1H » Wed Jan 15, 2020 9:26 pm

If the problem doesn't specify, either should be fine to use. Although, if you are given concentrations then you are likely to use Kc rather than Kp, or if the problem mentions a gas, you would use Kp for partial pressure

Verity Lai 2K
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Joined: Sat Aug 24, 2019 12:18 am

Re: When to use K and Kp

Postby Verity Lai 2K » Wed Jan 15, 2020 10:09 pm

In a peer review session, the UA suggested that we should use Kc unless it specifically tells us to find Kp or gives information using atm or bars.

MAC 4G
Posts: 121
Joined: Wed Sep 18, 2019 12:16 am

Re: When to use K and Kp

Postby MAC 4G » Wed Jan 15, 2020 11:30 pm

And another thing to look out for, even if the question doesn't specify whether or not it wants Kc or Kp look at the given equation. If the reactants and products have "(g)" next to them, you'll look to find Kp because they're gases and you would use the partial pressures for it.

Daniel Yu 1E
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Joined: Sat Aug 24, 2019 12:15 am

Re: When to use K and Kp

Postby Daniel Yu 1E » Thu Jan 16, 2020 10:16 am

Maya Pakulski 1D wrote: This might be a dumb question but you calculate all of these the same way right, with products/reactants?

Yes, although you might have to do some other calculations to get everything in the same units.

Madelyn Romberg 1H
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Joined: Tue Oct 02, 2018 12:16 am

Re: When to use K and Kp

Postby Madelyn Romberg 1H » Thu Jan 16, 2020 10:25 am

Typically it will specify. When given all gases, you will likely use partial pressure. If they specify concentration when given gasses, you may need to use PV=nRT to convert between the two. K is a general symbol which can apply to Kp or Kc. In this class he has had us specify which we are using.

Angela Patel 2J
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Joined: Sat Aug 24, 2019 12:17 am

Re: When to use K and Kp

Postby Angela Patel 2J » Thu Jan 16, 2020 10:48 am

What if you are given all gases, can you still use Kc? I know you can convert to Kp but why wouldn't we just use concentrations if they are given?

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

Re: When to use K and Kp

Postby Bryce Barbee » Thu Jan 16, 2020 11:14 am

I was told that Kp can be used for gases and Kc can be used for aqueous solutions. I believe that Kc can be used for gases as well if given concentrations but I am also unsure about that.


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