## R Constant

$PV=nRT$

Leslie Almaraz 4G
Posts: 99
Joined: Fri Aug 02, 2019 12:16 am

### R Constant

How do you know which variation of the R constant to use?

Jacey Yang 1F
Posts: 101
Joined: Fri Aug 09, 2019 12:17 am

### Re: R Constant

It depends on the units for pressure and volume given in the problem.

Bryan Chen 1H
Posts: 58
Joined: Mon Jun 17, 2019 7:24 am

### Re: R Constant

on the equations sheet look at the units for R and make sure they match up with those given in the problem, or those that you may convert to/use

RRahimtoola1I
Posts: 102
Joined: Fri Aug 09, 2019 12:15 am

### Re: R Constant

Here are the different gas constants. It depends on the units you are using in the equation. For PV=nRT you would usually use the 0.082.
Attachments

Edmund Zhi 2B
Posts: 118
Joined: Sat Jul 20, 2019 12:16 am

### Re: R Constant

The R constant will vary based on the other units given to us within a problem. Our formula sheet should always have a value of R that we will need to use in any problem on an exam.

Rory Simpson 2F
Posts: 106
Joined: Fri Aug 09, 2019 12:17 am

### Re: R Constant

Just make sure that you choose the right R constant depending on the units for pressure and volume, or convert all the units so that you can 0.082 L*atm*mol^-1*K^-1.

Jasmine Vallarta 2L
Posts: 102
Joined: Sat Aug 17, 2019 12:18 am

### Re: R Constant

it depends on the units of pressure given to you in the problem

Michelle N - 2C
Posts: 117
Joined: Wed Sep 18, 2019 12:19 am

### Re: R Constant

Leslie Almaraz 4G wrote:How do you know which variation of the R constant to use?

I know that Test 1 is already over, but in the equations sheet that Dr. Lavelle provided, there were many variations of it. To answer your question, the best way to know which R constant to use is to see the units used in the problem. If it mentions atm, then it'll be the number with atm in the units. Same applies for J, and so forth.

Shail Avasthi 2C
Posts: 101
Joined: Fri Aug 30, 2019 12:17 am

### Re: R Constant

The value of R you use depends on the units given to you in the problem and the units which your answer needs to be in. The units of R will cancel out with all of the given terms to give you your final answer's units.

Maria Poblete 2C
Posts: 102
Joined: Wed Sep 18, 2019 12:15 am

### Re: R Constant

In the equation sheet we're provided with, there are a number of different values to use for the R constant. It's important to look at which units are being used, which will tell you which one is appropriate to use.

SarahCoufal_1k
Posts: 102
Joined: Thu Jul 25, 2019 12:17 am

### Re: R Constant

It depends on the units of the other. variables provided. Choose the r with the matching units and all but the variable you are looking for should cancel out.

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

### Re: R Constant

Depending on the units given, use the R constant that uses the same units in order for them to cancel and give the desired answer.

RichBollini4G
Posts: 100
Joined: Wed Sep 18, 2019 12:18 am

### Re: R Constant

Leslie Almaraz 4G wrote:How do you know which variation of the R constant to use?

I would say look at the specific units of the problem.

RichBollini4G
Posts: 100
Joined: Wed Sep 18, 2019 12:18 am

### Re: R Constant

Shail Avasthi 3C wrote:The value of R you use depends on the units given to you in the problem and the units which your answer needs to be in. The units of R will cancel out with all of the given terms to give you your final answer's units.

Thank you

Mandeep Garcha 2H
Posts: 100
Joined: Sat Aug 24, 2019 12:17 am

### Re: R Constant

It depends on the units given in the problem.

Anushka Chauhan2B
Posts: 51
Joined: Sat Aug 24, 2019 12:16 am

### Re: R Constant

The one with similar units in the problem so that the units can cancel

Indy Bui 1l
Posts: 99
Joined: Sat Sep 07, 2019 12:19 am

### Re: R Constant

The R constant is dependent on the units of pressure you are given. Looking up a table is helpful and just pay attention to the units you are given in the question. You don't need to memorize this, just know which values correspond to each unit of pressure.

kendal mccarthy
Posts: 109
Joined: Wed Nov 14, 2018 12:22 am

### Re: R Constant

To determine which R to use view the givens you have and then you can determine which R unit would cancel out the appropriate units to get what value you desire. For most calculations, like in the VP=nRT equation, it will be 0.08206.

vanessas0123
Posts: 100
Joined: Wed Sep 11, 2019 12:17 am

### Re: R Constant

Look at the units you have and match it with the R constant's units!

Micah3J
Posts: 100
Joined: Tue Oct 08, 2019 12:16 am

### Re: R Constant

Just make sure that the R constant and your given units will cancel out and match accordingly

Orrin Zhong 4G
Posts: 51
Joined: Sat Jul 20, 2019 12:16 am

### Re: R Constant

There are a lot of gas constants, so just fit the units that are involved with the units of the correct gas constant. Generally, I use 0.0821 Latm/(molK) when I'm trying to find volume or pressure and 8.314 J/(molK) when I'm trying to find energy.

Joanne Lee 1J
Posts: 100
Joined: Thu Jul 25, 2019 12:15 am

### Re: R Constant

You can decide which form of R to use based on what the units of the given values are.

Charlene Datu 2E
Posts: 62
Joined: Wed Sep 11, 2019 12:16 am

### Re: R Constant

When looking at the units, it's good to note which ones will cancel out, and to keep in mind the units that your answer is supposed to be in. For the ideal gas law, you will typically be using any value with a unit of pressure (atm, bar, Torr). When calculating anything related to energy, the values with units of J or L/atm (1 L atm = 101.325 J) are helpful.

Jasmine W 1K
Posts: 49
Joined: Sat Sep 07, 2019 12:18 am

### Re: R Constant

It depends on the units given in the problem. All of the R constants mean the same thing; the numbers just change due to unit conversions.

Jose Robles 1D
Posts: 100
Joined: Fri Aug 02, 2019 12:15 am

### Re: R Constant

Read the problem and see the units being used in the question, look at the pressure usually.

Gurmukhi Bevli 4G
Posts: 49
Joined: Wed Nov 14, 2018 12:20 am

### Re: R Constant

It will normally depend on the units given for the other quantities being used in the problem, and the variations of R and its value/units will usually be given on the formula sheet, so it is easier to assess the units on a case by case basis and see which one is the best fit.

Tahlia Mullins
Posts: 105
Joined: Thu Jul 25, 2019 12:15 am

### Re: R Constant

I always just look at the units given, and it’s usually pretty easy to tell. Sometimes, temperature might need to be changed to Kelvin though!