Units for R


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Harmony Becerra
Posts: 32
Joined: Sun Jan 21, 2018 3:00 am

Units for R

Postby Harmony Becerra » Sun Feb 17, 2019 11:26 pm

For the R constant, what exactly are the units? I've always thought they were J/Kxmol but could it also be kJ/Kxmol?

MadisonFuentes1G
Posts: 52
Joined: Fri Sep 29, 2017 7:04 am

Re: Units for R

Postby MadisonFuentes1G » Mon Feb 18, 2019 12:17 am

The constants and equations sheet show that there are a couple of ways to write out the units.

Maya_Peterson1C
Posts: 62
Joined: Fri Sep 28, 2018 12:28 am

Re: Units for R

Postby Maya_Peterson1C » Mon Feb 18, 2019 9:51 am

There are different values for the constant R depending on the units used in the problem.

Ibrahim Malik 1H
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Joined: Fri Sep 28, 2018 12:27 am
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Re: Units for R

Postby Ibrahim Malik 1H » Mon Feb 18, 2019 10:01 am

Depending on which value you use, R can have the constants: J*K-1*mol-1, L*atm*K-1*mol-1, L*bar*K-1*mol-1, or L*Torr*K-1*mol-1. You use the various values of R based on the other variables used, make sure all the units cancel out and you are left with the units you are trying to find.

705170809
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Joined: Fri Sep 28, 2018 12:26 am
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Re: Units for R

Postby 705170809 » Mon Feb 18, 2019 3:06 pm

It depends on the information you are given, and ultimately what you are solving for.

Brian Hom 2F
Posts: 60
Joined: Fri Sep 28, 2018 12:24 am

Re: Units for R

Postby Brian Hom 2F » Mon Feb 18, 2019 3:09 pm

The units for R vary depending on which of the Rs you want to use. Usually you will be using 8.314 J/molK or 0.08206 Latm/molK. Make sure to look at what the problem gives you and what the problem wants in regards to units.

Karan Thaker 2L
Posts: 75
Joined: Fri Sep 28, 2018 12:26 am

Re: Units for R

Postby Karan Thaker 2L » Mon Feb 18, 2019 4:44 pm

You have to approach it depending on what you want to cancel out within the context of the problem. Choose the R value with units that will cancel out whatever form of units you have already been given.

Cole Elsner 2J
Posts: 88
Joined: Fri Sep 28, 2018 12:25 am

Re: Units for R

Postby Cole Elsner 2J » Mon Feb 18, 2019 4:47 pm

These units vary. Always write out your units for calculations, just so you know what R value is needed to solve. In order to get the write answer you need to use the correct R based off of what's asked for and what units are given.

Kyither Min 2K
Posts: 60
Joined: Wed Oct 03, 2018 12:15 am

Re: Units for R

Postby Kyither Min 2K » Mon Feb 18, 2019 7:43 pm

There are various ways in which one can use the constant R and so there are various units for the constant. For example, in the PV=nRT equation, one side has atm*L and the other as mol*K*R, and so to cancel so they equal each other, R has the unit and value of 0.08206 atm*L/mol*K. However, for work, w= nrTln[(v2-v1)] and so we need the final result to have joules as the unit so R has the value and unit of 8.314 joules/mol*K .

Jonathan Pai 2I
Posts: 121
Joined: Fri Sep 28, 2018 12:27 am

Re: Units for R

Postby Jonathan Pai 2I » Mon Feb 18, 2019 8:32 pm

using which R depends on if the answer is looking for joules or looking for something else, like liters per mol. But, you can always convert after using 101.325 to get the correct units and value

Heidi Ibarra Castillo 1D
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

Re: Units for R

Postby Heidi Ibarra Castillo 1D » Sat Mar 16, 2019 8:31 pm

depending which R you used is also dependent on the units you have, at the end most should be able to cancel all out


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