Gas Constant Value

[Audra Mcleod 3G]

Hello!
I was wondering which gas constant we're supposed to use in this class when doing calculations with the ideal gas equation. I know there's multiple values for the gas constant, but the one I've seen most used in this class seems to be .08205. So is this gas constant the one we'll predominately use, or should I memorize all gas constants in case we have to use a different value (depending on units)?

[Margia Adriano 2A]

Hi there! Which gas constant value you use typically depends on what the units you're working with are. For most of the problems I've seen that would be the one we're using the most so I think it would be fine to stick with that one, but it all depends. Hope this helps, and please correct me if I'm wrong!

[Samuel Flores 1E]

Hello! On the "Constant and Equations" sheet (found on Professor Lavelle's website), the sheet has all the different gas constants for different units that may arise. I believe we are permitted to use the Constants and Equations reference sheet on the midterms, so you can simply refer to the sheet if you need to know a gas constant for a question.

Hope this helps!

[Lorraine Medina 3E]

Hi! the gas constants are on the constants and equations sheet found on Lavelle's website, and we can use that sheet during tests. therefore, you don't necessarily have to memorize all of them if they are on the sheet, but I guess use the one that has the correct units for the problem. Hope this helps!

[Serena Song 1A]

Hi! The value we use for R generally depends on the units! .08206 (L atm)/(mol K) and 8.314 J/(mol K) are probably the ones we'll use most tho. Just make sure that the units on the right and left are the same, and you'll be good!

[Namita Shyam 3G]

During exams, we can use an equation sheet (which is on professor's website) that contains I believe three R-values... Those are the only R-values that we are given to use on exams, from what I've heard. However, those three given R-values are all we need to do most problems, so I would recommend practicing using those values!

[Kiyoka Kim 3C]

https://lavelle.chem.ucla.edu/wp-conten ... ations.pdf. This has the gas constant value with different units!

[Sara Sandri 2B]

Hey! To answer your questions, you have to look at the units of the other components of the problem in order to make a decision on what gas constant you want to use. Most of the time, pressure is in atm so we want to use the gas constant 0.0821 (L atm)/(K mol). If our pressure was in kPa or mmHg, we would use the gas constants that correspond to those units.

[Alen Huang 2G]

To decide which one to use you would need to look at the units for the values that you calculated/given and use the constant that matches those units.

[Alex Benson]

Hi! With the gas constant vary, and you just need to make sure that the units line up!

[Julianna Shimabukuro 1D]

The gas constant value will be on the equations sheet that we are allowed to use on the midterm and final. Although there are different R values with different units, you use the one that has the correct units necessary to cancel or that goes with the problem.

[Lung Sheng Liang 3J]

Hello, for this class we should be using the gas constant given in the equations/formula sheet Lavelle provided us for exams. We don't need to memorize it!

[Chinmayi Mutyala 3H]

You would have the check the pressure units to figure out what constant to use and you don't need to memorize them because they can all be found on the Constants & Equations Sheet on Lavelle's website.

[Hasan Mirza 3F]

Just check the units and use the corresponding value on the equation sheet!

[Alexis Sanft 1E]

Does anyone know if Lavelle is also strict on significant figures? I just want to make sure that I do not loose easy points on the midterm, so if anyone who has taken him previously could say, I would appreciate it!

[Namita Shyam 3G]

Does anyone know if Lavelle is also strict on significant figures? I just want to make sure that I do not loose easy points on the midterm, so if anyone who has taken him previously could say, I would appreciate it!

I didn't have him previously, but I asked a couple TAs and they told me not to worry about it! So you should be fine!

[Charlotte Chen 3B]

Does anyone know if Lavelle is also strict on significant figures? I just want to make sure that I do not loose easy points on the midterm, so if anyone who has taken him previously could say, I would appreciate it!

Also, the midterms are multiple choice so usually you should be able to select the answer you got even if it's a few significant figures off! But just in case, I would generally use exact values until you get to the final answer to avoid possible rounding errors

[kentbui1d]

The value is on the formula chart, and like what others have said make sure the units are correct!

[DPatel_2L]

Use the one that matches the units

[Adam Bustamante 1I]

The two gas constant values (that I know of) are 8.314 J/(mol x K) and 0.08206 (L x atm)/(mol x K) and I think it just depends on what units the problem is asking the answer to be in, along with what units the problem gives to you. Both are on the equation sheet we're allowed to use during the midterms and final.

[Jason Knight - 1F]

When determining which gas constant value to use we have to consider the units given in the problem. We have (R=8.314 J*K^-1mol^-1) and (R=0.08206 L*atm*K^-1) as our two gas constant values, and matching units to make sure they cancel in the problem is essential for receiving the desired output.

[Pranav Daggubati 3C]

You must look at the units you are working with to determine this because each gas constant has different units.

[derickngo3d]

Based on the units, goose the appropriate gas constant-value.

[Kristina Krivenko 3I]

Since there are several different values for the gas constant that differ, depending on the units, look at the units you are dealing with in the problem and choose the appropriate R value (that is, make sure that units match up). The best way to double check whether you chose the correct value for R is to make sure all units cancel out when you do your calculation.

[Simi Kapila_3E]

All the gas constants are on the equation sheet, and you will be able to figure out which one is the proper one to use by looking at the units and seeing if it corresponds with the rest of the units you are using in your problem.

[George Hernandez 3I]

It all depends on the problems. Some discuss certain units so you would use the constant that include those said units.

[Jordan Tatang 3L]

It depends on what units are given on the problem and you can work based off of that.

[Hailey Kang 2K]

Hi! It all depends on what is given in the problem. Usually the first thing I look at is the units of pressure. If there is no pressure given, I will go with the R value that has no pressure in the units!

[Chloe Shamtob 2H]

The gas constant you are suppose to use always depends on your units. Make sure to write down your units when doing a problem to make sure not to mix them up. The way I do it is I look to see if the values are in L.atm or joules. This helps a lot. Make sure things cancel out in the end or you will get the wrong value.

[Thomas Vu 1A]

What examples are there for using R=8.314 J*K^-1mol^-1) because I'm still kind of confused why it seems to be used interchangeable with the other R value

[Joey_Okumura_1E]

What examples are there for using R=8.314 J*K^-1mol^-1) because I'm still kind of confused why it seems to be used interchangeable with the other R value

R = R=8.314 J*K^-1mol^-1 is used, for example, when trying to find the work done by a isothermal, reversible system (w = -nRT ln (V_f/V_i). The different R values are not interchangeable because the units are different. A shortcut to determining the appropriate R value is to look at the units of the other components of the equations. Units, just like numbers, can cancel each other out.

[Jason_Glass_2L]

What examples are there for using R=8.314 J*K^-1mol^-1) because I'm still kind of confused why it seems to be used interchangeable with the other R value

A good way to understand the difference between the two is that the one with the one with the L atm unit can be multiplied by the conversion of 1 Latm=101.325 J on the equation sheet to equal the one with the Joules unit. So, just check which units align with the corresponding R value units.

[Ryan Agcaoili 2E]

The gas constant values are .08206 (L atm)/(mol K) and 8.314 J/(mol K). They both count as R, but make sure to remember the difference in using both of them. The first R value is used for problems dealing with ideal gas constant (so the equation PV = nRT). On the other hand, the second value is used for energy (note that the units cancel out and joules is left).

[VSU_3F]

Yes, as everyone mentioned above, you must first check the units! That's the most important thing. But now that we're doing a lot of thermodynamics and work problems (which has the unit of Joules), we'll be using R= 8.314 J/Kmol a lot more often.

[Victor Qiu 1C]

I think 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)

[Katie Phan 1K]

I don't think you need to stress that much over it (at least for tests) since it's on the formula sheet Lavelle provides.

[Ken_Cheng_2A]

Hi, a lot of people are saying just to look at the units and use the one that matches or cancels out nicely, and I guess I'd just like to comment on how this "follow the units" idea can be really helpful for many other chemistry problems. Sometimes, if you read a question and have no idea how to answer it, you can just see all the given values from the problem and their corresponding units, then look for a formula or two that allows you to somehow cancel out all the units until you are left with one corresponding to the answer you're supposed to find. Of course, this won't be applicable to every question out there, but it's a good place to start if you're completely stumped by a question!

[Aria Movassaghi 1A]

They're all on the sheet we get for exams so no need to memorize, however you should be familiar with how to use them depending on units.

[Shana Patel 1C]

The units usually depend on the problem being solved, and the other units given in the question. The units are usually given on the exam sheet, so we just need to know how to apply everything.

[Crystal Pan 2G]

You decide which value to use by looking at the units. You choose which is the most desirable to get the units of the value you want.

[Morgan Gee 3B]

The different gas constants are based on the units that make them up. As a result, determine the units that are given/desired and pick your gas constant based on that value.

[Edwin Liang 1I]

Hello! there are multiple forms of it depending on the units needed.

[Britney Tran IJ]

there are different values, but use the one that corresponds with the units given

[David Y]

The gas constant you use depends on the units given in the problem.