R ideal gas constant

[Isabelle Hales 1J]

Hi! While doing the weekly sapling hw, I noticed that there are two values for the R ideal gas constant. I do not remember going over this in class but could someone please explain when I should use each different value? I know this is very basic material but it will really help!

[Olivia Smith 2E]

I'm not exactly sure which instance you are referring to, however, it may be because of different units used to convert it!

[Varsha Ravi 3E]

The different values of R are for different units used in the rest of the problem! On our formula sheet, it has all the different values for R along with the units used with each value.

[Sofia Azmat 1I]

The different values for R are given to you for different units, and you just have to use the given values accordingly.

[Isabella Chou 1A]

I agree with everyone, there are different values of R because these values have different units, so you just need to make sure that you are using the R value that will leave you with the correct units in your answer.

[Ziyan Peng 3A]

I agree with what everyone here is saying! Notice how the units for the two units as seen on the equation sheet are different. What R value to use depends on what other units (e.g. for pressure) we are using in the specific question.

[Justin Zhang_1A]

The different R values are for different units, so you should use the one that fits the units given in the question.

[Bella Bursulaya 3G]

Depending on the units given, you'll use different R values OR you could convert other things in your equation to get them to the same units as your desired R. Just be careful when using 0.0821 L*atm/mol*K because you need to use 101.325 J = 1 L*atm to get J, while 8.314 J/mol*K will give you J right away.

[Navdha Sharma 3J]

the different values of R just correspond to the different units. Just being aware of the units in the problem helps to know whether to use 8.314 or 0.0821 as the R value.

[Morgan Gee 3B]

There are different R constants based on the units they have. For example, 1.00 atm = 101.3 kPa. While R may be 0.082057 atm L/molK, it would be 8.31 kPa L/mol K (which if you notice is the same as 8.31 J/mol K)

[Joshua Eidam 2A]

Base it off of the units given/ the units you want for your answer. This will determine which R value you should use.

[Ariel Guan 1H]

whichever one you use will depend on the units that are given in the problem

[Victor Qiu 1C]

It depends on the units in the problem. I think we should use the value of R whose units are the same as the units in the problem.

There are 4 values that are used more often:
R = 0.0821 L·atm/(mol·K) = 8.3145 J/(mol·K) = 8.2057 m3·atm/(mol·K) = 62.3637 L·Torr/(mol·K)

[Sharon Kim 2A]

Usually the R constant that is 0.0821 L·atm/(mol·K) is used when dealing with PV=nRT. The other gas constant 8.314 J/(mol·K) when dealing with equations like w=-nRTIn(T2/T1). But of course, make sure you are using the units corresponding to the question.

[JaesalSoma1E]

Just check the units in your problem before deciding which one to use. A general trend however is that 0.0821 is used in PV=nRT problems and 8.314 is used in energy (work and thermodynamics) problems.

[Nina Fukui 2J]

They are both on the formula sheet and you have to be careful with the different units you're dealing with in your equations. One has J*K^-1*mol^-1 while the other has L*atm*K^-1

[Nishka Vipul 1J]

Hi! On the equation sheet, we are given a couple different values of R. The key thing to notice when choosing which R value to use is the units! Depending on what we are calculating/what we want to get to/what is given in the question, we can choose the R value accordingly, based on units. Hope this helps!

[Zainab Jamali 1H]

This always trips me up when I'm trying to work quickly haha! The most definite way to know is to look at the units in your calculation and compare them to the units of the two different constants (they are very different!). Hope this helps :)

[Joshua_Chan_3K]

I'm pretty sure that all the sapling homework problems used the same value of R (8.314) but this does differ from the one we learned of 0.0821. Really the only difference is in the units used for pressure. The first is based on using barr while the second is based on using atm which is what Lavelle said we would be using mostly in this class. It's a bit confusing because they simplify the units in a way that removes the pressure (I don't even understand how they do this), but really for our purposes just treat 8.314 as the R used in the thermodynamics equation while 0.0821 is used in ideal gas equations (PV = nRT). However, its good to check the units in the problem every time as you need to use a different R based on the units. Another way that I prefer is to just use 8.314 and convert pressure to barr every time but thats personal preference.

[Charmaine Ng 2D]

I get confused over this too ahh but I think usually 0.08206 is used for PV=nRT and 8.314 for other cases. This is super general though, so it's safer to go by units and seeing what will cancel out! :))

[Michael Cardenas 3B]

I believe the two different R values are because of the different units represented in each.

[Hannah Lechtzin 1K]

You should check your units to figure out which R value to use! 8.314 is for calculations that include Joules, while the others are for various forms of pressure. Try looking at the units of your calculations and match them up to the correct R value.

[Jose Miguel Conste 3H]

it really depends on the units given for the problem, that would be the correct R to use

[Gabe_Ek 1G]

Yes like most people said there is two different R constants to use. You should either one accordingly based on which values are presented in the problem to get the appropriate answer.

[Aria Movassaghi 1A]

Depending on the units in your equation, different r values will be needed.

[apurva-3E]

Look at the units you are given and then select the gas constant with the same units.

[Edgar Velazquez 2K]

Which value you use depends on the units of the problem. Always make sure that the units of the R value will cancel out the other units. If they don't, then you know that you're using the wrong value.

[George Hernandez 3I]

It all depends on what values are present in the problem. The constant aims to cancel out most of them

[Jose Miguel Conste 3H]

It will depend on the units you are given by the problem in order to figure out which R to use

[Bai Rong Lin 2K]

It is based on the problem and the unit that is given. It would be ideal that the unit would cancel out by the units of R value.

[Jarrett Sung 3B]

Make sure you check to see what the units are for the question, because the R value depends on the units used.

[Andrew Dao 3C]

They have different units so you will have to use them depending on what the problem asks of you.