R Constant

[Claire_Latendresse_1E]

Hey guys!
I'm struggling a bit with picking which R value to use (8.314 J mol^-1 K^1 versus 0.08206 L atm mol^-1 K^1). I'm assuming that we use 0.08206 whenever we do a calculation with atmosphere as units like in most PV=nRT problems. Is that correct?

[Selena Quispe 2I]

You choose the R that matches the unit from your Pressure. If the problem gives you torr then use the R constant with torr and if you are given a pressure in atm then use the R constant with the atm unit. I hope this helps!

[Nayra Gharpetian 3F]

there are several values of R and the only way we know which one to pick is by looking at the units. match the units of the info they give to the units in R

[Jordi M 2I]

Yes, look at the units the problem gives you. Most of the time though it will be atm. Your equation sheet will have all of them though.

[SophiaJenny3I]

Hi! You just have to look at the units the problem gives you. Normally, it's deciding between the one with bar and atm, and the problem will tell you which to use! If you're ever uncertain, write out all the units when you're calculating a value using R and double check that the units cancel and you're only left with the unit of what you're solving for.

[Ximeng Guo 2K]

In the equation pv=nRT, if p is in pascal and v is in m^3, use 8.314; if p is in atm and v is in L, use 0.08206.

[Sana Nagori 2H]

writing out your units is always helpful in calculations so you can keep track of what cancels out and whether you end up with the correct units needed for you answer.

[Isabella Cortes 2H]

I typically look at the units for the pressure value that has been given to determine which R value to use

[ellenulitsky Dis 1I]

I just look at the units and see what matches up with it from the constant sheet given to us! Hope this helps.

[Abhinav Behl 3G]

Picking the right R constant to use is as easy as identifying the units that are given in the question. Essentially, you want most of your units in the PV=nRT equation to cancel out, leaving you with just the unit for whatever the question is asking for. So, always pick the R constant that contains units that match the units given in the question.

[Grace_Remphrey_2J]

Selecting the correct R constant can be determined by the units used in the calculations. It's super helpful to keep track of units through your calculations so you can choose the right R constant. Hope this helps!

[Elizabeth Kaplan 3I]

Hi! I'm pretty sure that the only difference between the R constants is the units for pressure. So, although we say 1 bar=1atm, you would choose two different values for R because bar and atm are not exactly equal.

[dana hu 1B]

Hello,
it would depend on what your given and final units are and what units need to be canceled out. To list a few often used units of R are 8.314 4621(75) J K−1 mol−1, 5.189 × 1019 eV K−1mol−1, 0.082 057 46(14) L atm K−1 mol−1,1.985 8775(34) cal K−1 mol−1, 1.985 8775(34) × 10−3 kcal K−1 mol−1, etc.

[Nicoli Peiris 1B]

You chose the R value that matches the rest of the units of your values.

[Gabriel Nitro 1E]

Hi,

Yes. BUT! As a bookkeeping rule it is always useful to look at what units you have presented in front of you along with the units the problem is asking you to solve for. This way, you'll be able to make sure the proper units cancel out to get what you want, whether you want atm or J.

Hope this helps! :)

[My-Lan Le 1L]

Like the other comments say, you would just have to look at the given information and choose the R that matches the units present. So, in the end, you could cancel the units, ending with the units that the question asks for.

[DPatel_2L]

You chose the one that matches the units of your other values

[Kayle Lim 2C]

The different constants for R just differ in units, so always choose the constant that best fits with the units presented in the problem. There is a list of the different type of R values and their correlating units on our given equation sheet, so don't worry about having to convert them. It's super important that you do not mix up units though, so be sure you're checking your units throughout the problem solving process and choose the value you think would best fit!

[Brian Bui 3H]

Like others said, I would try to look at the units of the other terms that you're given. I think it's a pretty good to determine which R constant you need to use :^)

[shevanti_kumar_1E]

Something really helpful for me is looking at the units and making sure they cancel out. In the formula sheet it mentions the units for both R values. Your units should cancel out if you picked the right one.

[Ephrem Gerald 2A]

Yes, you are correct to look at the units to determine which value for R you would need to use. When you are dealing with energy you would use the 8.314 value and when you are dealing with ideal gases and units such as atm and L, then you would use 0.08206.

[Aayushi Jani 3A]

You should choose the R value for which the units cancel out so that the only units that remain in the overall equation are the ones for the variable you are trying to solve for. It is definitely helpful to write out all the units and then physically cross them out so that you can clearly see which units you are left with and whether or not they match the units that you are trying to solve for.

[Lorraine Medina 3E]

I would use the R constant that matches the units given in the problem. Hope this helps!

[Mary Shih 3J]

R values account for units so choose the number with units that correspond to the question

[Ariel Guan 1H]

You should use the R value that matches the units that are given in the problem so that they can cancel out.

[aashmi_agrawal_3d]

In order to decide, just look at the units the problem gives you and see which one matches up with the units in the R constant.

[Anya Holbrook 1E]

I'm not sure if this works for all occasions when you are using PV=nRT, but I found that when looking for work I have used the 8.206x10^-2 L*atm*K^-1*mol^-1 R constant and converted my final answer to J instead of using the 8.314 R constant and got the same answer. So I don't know if this would work in other situations, but I hope this helps!

[austin-3b]

That is correct. However, when you use the constant to find work (joules), then you use 8.314.

[Jordan Tatang 3L]

you should look at the units that are given in the problem and work based off of that

[Alen Huang 2G]

If you take a look at the units you are given in the problem you should find an R constant that matches those units.

[DavidTabib 3H]

You should always look at the units in the problem and choose the R constant from there

[Isabel_Eslabon_2G]

Whichever R value you use depends on the units of the other values you are given in a problem.

[Simer_Shera_2D]

There are several forms of R like others have said. I think for this unit, we use the same one (the one you mentioned) but I'd pay attention to the units when solving problems just to be sure.

[Nick P 3D]

The two most common forms of R use pressures in either Torr or Atm, you just use whichever value of R matches the units with the information you are given in the problem.

[Britney Tran IJ]

the r value you will use will depend on the units given in the problem

[Yu Jin Kwon 3L]

I know there are already a ton of responses on choosing an R constant based on the units given in the problem, and sometimes this is really hard to identify in a way too. The biggest thing that helps me is writing down the units IN the equation itself so I can see what could cancel out visually rather than just looking at which units are available in the problem.

Hope this helps!

[Laura 3l]

Yes, pay attention to the units and match them up!

[Alisa Nagashima 1B]

Yes, it's helpful to always keep track of units to determine which R to use. They should cancel out accordingly

[Sai Ramadas 1J]

You can pick the R value based on the units provided in the question. A good way to check that you did it right is to check whether you got the correct units for your final answer.

[alexandralopez 3F]

HI! you should pick the R value that has the correct units necessary to solve the problem!

[Ryan_Kien_1L]

You pick the R that has matching units that cancel out all the other units in the equation.

[Annie Liang 3D]

You would choose the R constant that corresponds with the units you are using in the equation.

[Lung Sheng Liang 3J]

Generally, you should use the value of the R constant that has the same units as your problem.

[Bryan Le 2K]

In my experience, the best way to figure out what R constant to use is to look at the units that I am given. From there, I pick the appropriate R constant to matches with the units.

[Simran Bains 2C]

If we are given pressure in torr, we use 8.314, if we are given pressure in atm, we use 0.08206.

[joshtully]

Correspond R with the units in the problem.

[Gustavo_Chavez_1K]

Yeah we just meed to make sure that the units of the R match the units given in the problem.

[Sondia Luong 1C]

If you're using R in the PV = nRT where n is in moles and L is in liters, you'd typically use 0.08206 because it's in (L*atm)/(mol*K). I find myself often using 8.314 for q = m*C*delta T because the units are in J/(mol*K). However, as everyone says, it depends on what units you are using!

[Hannah Lechtzin 1K]

My preferred way of picking an R constant is through looking at the units. I know if I'm solving for something with L and atm, then I'll use 8.206x10^-2 or if I'm solving for energy in J I'll use 8.314. I hope this helps!

[Javier Perez M 1H]

Definitely keep in mind the units. Atm seems to be the most common.

[Aanya Tanti 3C]

Choose the R value that matches the units you have- try to cancel everything out to check.

[Daniel Hernandez 1G]

Most of the time what I find useful is matching the units of the problem with the units of the R constant.

[Michael Cardenas 3B]

Whichever units for the R value match your units will decide which R you have to use.

[Anthony_Sandoval_1D]

You choose the R-value that matches your units which seems to usually be atm. It all depends on what is given to you in the problem.

[Constance Newell]

Check the units first! You wanna zero everything out

[Jared Limqueco 3E]

I always write my units down even though it is tedious. Keep track of them to cancel out stuff to determine what constant R to use.

[Siwa Hwang 3G]

I believe that it depends on the context/equation youre using to solve the problem

[Abraham De Luna]

You have to take the units you are using into consideration when deciding which r constant to use.

[Jamie2002]

That's correct! Just pay attention to the units you are working with to figure out which to use. They should cancel out with the units of the other numbers.

[Hasan Mirza 3F]

Always check the pressure units and use the corresponding R value.

[LeahSWM 2E]

Yes, make sure to match the units always.

[alebenavides]

u check ur units and see what matches ur equation

[Nicoli Peiris 1B]

You chose which R to used based on the units you have for information given in the problem.

[Juwan_Madaki_3K]

The R constant you choose to do your calculations with is based on the units of pressure you're given. If you're given pressure in atm, then use the gas constant that has atm in the units.

[Megan Hulsy 1A]

You'd pick the R constant based on the units that are involved in the problem. Hope this helps!

[Kimiya Aframian IB]

Hey guys!
I'm struggling a bit with picking which R value to use (8.314 J mol^-1 K^1 versus 0.08206 L atm mol^-1 K^1). I'm assuming that we use 0.08206 whenever we do a calculation with atmosphere as units like in most PV=nRT problems. Is that correct?

Hi! I think the best way to check which R value must be used is to access the units being used in the problem from other values and considering what unit is in the desired output.You are correct in saying that 0.08206 is used in PV=nRT because it would cancel out L, atm, mol, and K. Hope this helps!

[Daniel Huynh 2J]

Yes, that is correct. You use R based on the units you have. For instance, you would use R = 8.206*10^2 L*atm*K^-1*mol^-1 if you want to start with atm.

[Brianna Chen 3F]

It depends on the units you are given so you would have to see what information is given and what you need to solve for.

[Emily_Stenzler_2H]

I also look at the problem and choose the units that match the pressure units in the problem!

[Ryan Agcaoili 2E]

A good tip when deterining when to use which R constant is to look at the units. 8.314 J/K * mol is usually used for PV=nRT, while 0.08206 L*atm / K * mol when dealing with pressure.

[Carly_Lipschitz_3H]

An easy way to figure out which R is to use is by matching the units in your equation with the units in the R value on the equation sheet.

[Chinmayi Mutyala 3H]

When there's pressure and volume involved in the calculation, I use the R constant that includes atm and L in the units. You just have to check the units and make sure it cancels out to get you the final units you need.

[Claudia_Danysh_2B]

When you're talking about P in atm, use R=.0821, and when you're talking about energy or work, use R=8.314

[James_Hankee_1C]

Look at the units the problem gives you. There are many R values so you must look at the units to find out.

[josephspindler2H]

You are correct in assuming that you use .08206 with atm, the other value is for use with energy or work (notice it has joules in its units). Like with most concepts in this class, units are very important and can be the deciding factor for which values are used.

[Jordan Tatang 3L]

Yeah, so there are a lot of responses to this question but it really just depends on the units that are given to you in the question and you would the R gas constant that cancels out those units.

[Victoria Dao 3G]

Like what a lot of people said above, when in doubt, just watch out for units!

[Vivian_Le_1L]

To figure out which R value to use, you pretty much look at the units involved. See which ones you want to match up/cancel out.

[Presley Gao 2C]

The R value you use is the one that cancels out the rest of your units - they are all equivalent, just in different units.

[Alejandro Gonzalez 2G]

I believe the R value you use depends on the units that are given to you and which ones the question asks you to end up with, whether it be J/K*mol, L*bar/K*mol, or any of the other possible values.

[Aria Movassaghi 1A]

The best way is to just match your units in the equation with the units for R

[Jason Knight - 1F]

Choosing the correct R-constant is an important decision when problem-solving, and can be simple when breaking down what other units are in the equation. When using our ideal gas law, we know to use (R=0.08206 L.atm.K^-1.mol^-1) because this will cancel out our units to solve for the unknown. Typically with work and entropy equations, unless we are using ideal gas laws, it is common to use (R=8.314 J.K^-1.mol^-1).

[Hasan Mirza 3F]

Try to match the units for pressure, atm or torr, with the ones given in the question.

[Juwan_Madaki_3K]

I usually look at the units of pressure given and use the R value containing that unit.

[Akriti Ratti 1H]

You should use the constant that matches the units you're working with.

[Anastasia Yulo 1C]

What helps in determining which R constant to use, is to be wary of the units that are being used!

[Mingzi Yang 1E]

I usually look at the unit of the pressure and use the R constant that matches the unit. So if the pressure is in atm, I use the constant that is 0.08206 L*atm*mol^-1*K^1.

[keely_bales_1f]

As students have mentioned above, the R constant you use depends on the context of the problem!

[Kiara Phillips 3L]

The units they give you usually give it away, but it you are in a time crunch I recommend just going with 8.3145 and then if you don't see your answer or if the numbers you are getting do not seem to make sense, use the other one.

[Jacob Schwarz-Discussion 3I]

You have to use the R value that matches up with your units. For example, when calculating work you would use 8.314 J. Look at the equation sheet and choose the R value that matches up with the units in your problem.

[eve444]

Usually I just go with the R value that matches the units required by the question. I believe the different R values are given in the constants and equations sheet.

[Sarthika Chimmula 3H]

Use the R constant that will help you cancel out the units mentioned in the problem.