partial pressures vs concentrations

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Jennifer Lathrop 1F
Posts: 71
Joined: Sat Dec 02, 2017 3:00 am

partial pressures vs concentrations

Postby Jennifer Lathrop 1F » Sat Jan 12, 2019 2:35 pm

I am still very confused on when to use the partial pressures or concentrations to calculate k. What will it say in the problem to suggest which to use?

Zenita Leang 2K
Posts: 67
Joined: Fri Sep 28, 2018 12:28 am

Re: partial pressures vs concentrations

Postby Zenita Leang 2K » Sat Jan 12, 2019 2:44 pm

You can look at the units that are given in the problem! If they give you mol/L (molarity) then you will use concentration to find K but if they give you torr, atmospheres (atm), or bar, then you will use partial pressure.

Sean_Rodriguez_1J
Posts: 62
Joined: Fri Sep 28, 2018 12:17 am

Re: partial pressures vs concentrations

Postby Sean_Rodriguez_1J » Sat Jan 12, 2019 2:45 pm

If the problems ask for Kc or Kp, that gives a pretty clear indication of what is desired. If they just ask for K, look at the units that they give. There is a good chance that you can figure out what they are asking for based on if the amounts given to you are in mol/L, atm, bar, etc. Also, the chemical equation itself could provide an extra suggestion (ex: all but one of the reactants and products in a reaction are gases, so converting the one non-gas's concentration to partial pressures would make sense, or the same situation but the reactants and products are mainly in aqueous solution).

Irene Zhou 1E
Posts: 73
Joined: Fri Sep 28, 2018 12:18 am

Re: partial pressures vs concentrations

Postby Irene Zhou 1E » Sat Jan 12, 2019 3:16 pm

It usually depends on the units that are given. If the reactants and products are all gases, then Kp can be used. However, it still may be easier to first calculate Kc because the question may provide numbers in terms of moles and liters.

Lauren Huang 1H
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am

Re: partial pressures vs concentrations

Postby Lauren Huang 1H » Sat Jan 12, 2019 5:15 pm

If the reactants or products are gases, then you can usually use either Kp or Kc. However, you can only use Kc for reactions involving aqueous solutions.


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