How to choose R

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705340227
Posts: 86
Joined: Wed Sep 30, 2020 10:08 pm

How to choose R

Postby 705340227 » Sun Jan 10, 2021 8:47 pm

During the discussion we went over how to choose the right R value but I am still confused so can someone please explain how to choose the right value of R? If you could give examples that would be perfect.

Ivan Chen 2H
Posts: 88
Joined: Wed Sep 30, 2020 9:48 pm

Re: How to choose R

Postby Ivan Chen 2H » Sun Jan 10, 2021 9:17 pm

The right gas constant R depends on the units for pressure and volume that the question uses. For example, if the question has the pressures measured in atm and the volume measured in liters, you would need to use 0.082057 L*atm*mol^-1*K^-1 for R.

Emily Tieu 2K
Posts: 38
Joined: Thu Jan 07, 2021 12:17 am

Re: How to choose R

Postby Emily Tieu 2K » Sun Jan 10, 2021 9:57 pm

The most common R values are 8.3145 J/(K*mol) and 0.08206 (L*atm)/(K*mol). Choosing which one to use depends on the given units of the other variables in the equation. For example, if the pressure (P) is given in units of bar pressure, you can convert bar pressure to atm using dimensional analysis and use R = 0.08206 (L*atm)/(K*mol) to solve. Another example would be if pressure is given in Pa, then you could convert and use R = 8.3145 J/(K*mol) to solve. Hope this helps :)

Gian Boco 2G
Posts: 81
Joined: Wed Sep 30, 2020 9:36 pm

Re: How to choose R

Postby Gian Boco 2G » Sun Jan 10, 2021 10:37 pm

Make sure the units for pressure and volume match(:

Dane_Beasley_1E
Posts: 68
Joined: Wed Sep 30, 2020 9:42 pm

Re: How to choose R

Postby Dane_Beasley_1E » Sun Jan 10, 2021 10:43 pm

In order to choose the right R you would make sure that the units for pressure and volume match the question.

Sarah Salam 1J
Posts: 55
Joined: Wed Sep 30, 2020 9:31 pm

Re: How to choose R

Postby Sarah Salam 1J » Sun Jan 10, 2021 10:59 pm

It depends on the units that are given in the question. One R value is in J/K*mol and the other is L*atm/K*mol, so you would look at what units are present or that you could convert to and use the corresponding R value.

Geethika Janga 1L
Posts: 78
Joined: Wed Sep 30, 2020 9:42 pm

Re: How to choose R

Postby Geethika Janga 1L » Sun Jan 10, 2021 11:02 pm

You would choose the value of R based on the units you choose to use for that particular problem. For example, if you look the the R value with units J/K*mol, then you are trying to cancel out a value with units "J" and if you would use the R value with the units L*atm/K*mol, when you are trying to cancel out a value with units L*atm.


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