R constant


Moderators: Chem_Mod, Chem_Admin

805097738
Posts: 180
Joined: Wed Sep 18, 2019 12:20 am

R constant

Postby 805097738 » Mon Jan 13, 2020 12:43 pm

When do we know when to use which R constant?

What are the two R constants and when are they used?

Is the unit for gas measured in atm pressure or bars?

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

Re: R constant

Postby Hannah Romeo 1J » Mon Jan 13, 2020 1:21 pm

R is used in the ideal gas law expression, PV=nRT. A specific R constant is used as a result of the given units in the problem. For example, if pressure has units of atm, R has a value of .0821 (L x atm)/(mol x K)

Jordan Ziegler 2J
Posts: 59
Joined: Sat Aug 17, 2019 12:15 am

Re: R constant

Postby Jordan Ziegler 2J » Mon Jan 13, 2020 5:23 pm

Units of gas can be expressed in atmospheres or in bars. However, the textbook uses mostly bars to express partial pressure. I would be prepared to do some conversions between the two units though.

Qiu Ya Wu 4I
Posts: 107
Joined: Fri Sep 20, 2019 12:17 am

Re: R constant

Postby Qiu Ya Wu 4I » Mon Jan 13, 2020 6:48 pm

Lavelle gives you 4 different values for the R constant on his formula sheet during tests. Whichever one you use depends on the units given in the problem.

Areli C 1L
Posts: 95
Joined: Wed Nov 14, 2018 12:19 am

Re: R constant

Postby Areli C 1L » Thu Jan 16, 2020 7:07 am

Qiu Ya Wu 4I wrote:Lavelle gives you 4 different values for the R constant on his formula sheet during tests. Whichever one you use depends on the units given in the problem.

Do you know if the problems will mention directly which R constant to use?(Like a given)

Sanjana K - 2F
Posts: 102
Joined: Sat Sep 07, 2019 12:17 am
Been upvoted: 1 time

Re: R constant

Postby Sanjana K - 2F » Thu Jan 16, 2020 9:18 am

It generally won't tell you exactly what R value to use, but all the constants are given in the formula sheet so depending on whether pressure is reported in atm or kilopascals, you'll know which R-value to use.

Areli C 1L wrote:
Qiu Ya Wu 4I wrote:Lavelle gives you 4 different values for the R constant on his formula sheet during tests. Whichever one you use depends on the units given in the problem.

Do you know if the problems will mention directly which R constant to use?(Like a given)

Sean Cheah 1E
Posts: 105
Joined: Wed Sep 18, 2019 12:20 am

Re: R constant

Postby Sean Cheah 1E » Thu Jan 16, 2020 9:37 am

As previous posters have already noted, pay careful attention to the units of the given values in each problem when determining which R constant to use. For example, when converting from Keq to delta G, the correct R value would be about 8.314 , which makes sense seeing as your final result should be expressed in Joules.


Return to “Ideal Gases”

Who is online

Users browsing this forum: No registered users and 1 guest