R Constant


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Leslie Almaraz 4G
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R Constant

Postby Leslie Almaraz 4G » Thu Jan 23, 2020 11:50 pm

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

Jacey Yang 1F
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Re: R Constant

Postby Jacey Yang 1F » Fri Jan 24, 2020 12:14 am

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

Bryan Chen 1H
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Re: R Constant

Postby Bryan Chen 1H » Fri Jan 24, 2020 6:23 am

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
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Re: R Constant

Postby RRahimtoola1I » Sat Jan 25, 2020 11:47 am

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.
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Edmund Zhi 2B
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Re: R Constant

Postby Edmund Zhi 2B » Sat Jan 25, 2020 4:52 pm

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
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Re: R Constant

Postby Rory Simpson 2F » Sat Jan 25, 2020 4:54 pm

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
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Re: R Constant

Postby Jasmine Vallarta 2L » Sat Jan 25, 2020 5:01 pm

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

Michelle N - 2C
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Re: R Constant

Postby Michelle N - 2C » Sat Jan 25, 2020 9:04 pm

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
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Re: R Constant

Postby Shail Avasthi 2C » Sat Jan 25, 2020 9:47 pm

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
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Re: R Constant

Postby Maria Poblete 2C » Sun Jan 26, 2020 12:31 pm

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
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Re: R Constant

Postby SarahCoufal_1k » Sun Jan 26, 2020 1:14 pm

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
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Re: R Constant

Postby Areli C 1L » Sun Jan 26, 2020 6:16 pm

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
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Re: R Constant

Postby RichBollini4G » Sun Jan 26, 2020 6:57 pm

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
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Joined: Wed Sep 18, 2019 12:18 am

Re: R Constant

Postby RichBollini4G » Sun Jan 26, 2020 6:58 pm

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
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Re: R Constant

Postby Mandeep Garcha 2H » Sun Jan 26, 2020 10:17 pm

It depends on the units given in the problem.

Anushka Chauhan2B
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Re: R Constant

Postby Anushka Chauhan2B » Sun Jan 26, 2020 10:19 pm

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

Indy Bui 1l
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Re: R Constant

Postby Indy Bui 1l » Sun Jan 26, 2020 10:20 pm

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
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Re: R Constant

Postby kendal mccarthy » Sun Jan 26, 2020 11:35 pm

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
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Re: R Constant

Postby vanessas0123 » Tue Jan 28, 2020 9:52 am

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

Micah3J
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Re: R Constant

Postby Micah3J » Tue Jan 28, 2020 10:02 am

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

Orrin Zhong 4G
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Re: R Constant

Postby Orrin Zhong 4G » Fri Jan 31, 2020 7:22 pm

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
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Re: R Constant

Postby Joanne Lee 1J » Tue Feb 18, 2020 9:21 pm

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

Charlene Datu 2E
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Re: R Constant

Postby Charlene Datu 2E » Thu Mar 12, 2020 5:26 pm

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
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Re: R Constant

Postby Jasmine W 1K » Thu Mar 12, 2020 6:49 pm

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
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Re: R Constant

Postby Jose Robles 1D » Sat Mar 14, 2020 5:44 pm

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

Gurmukhi Bevli 4G
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Re: R Constant

Postby Gurmukhi Bevli 4G » Tue Mar 17, 2020 11:50 pm

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
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Re: R Constant

Postby Tahlia Mullins » Wed Mar 18, 2020 12:16 am

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!


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