What does R stand for?

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Mike Matthews 1D
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What does R stand for?

Postby Mike Matthews 1D » Tue Jan 16, 2018 2:28 pm

The equation relating the heat capacity of an ideal gas at constant pressure and the heat capacity of an ideal gas at constant volume is:
Cpm=Cvm + R
That being said, what is R? Is it the gas constant? If so how does one go about deciding which value to use for R?

Kailey Brodeur 1J
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Re: What does R stand for?

Postby Kailey Brodeur 1J » Tue Jan 16, 2018 2:59 pm

R is the ideal gas constant. You decide what value of R you should used based upon what units you are using.

Jessica Nunez 1I
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Re: What does R stand for?

Postby Jessica Nunez 1I » Tue Jan 16, 2018 4:58 pm

As mentioned, R is the gas constant which is equal to . . .
8.314 J.K^-1.mol^-1 = 8.206 x 10^-2 L.atm.K^-1.mol^-1 = 8.314 x 10^-2 L.bar.K^-1.mol^-1 = 62.364 L.Torr.K^-1.mol^-

Nicole Jacobs 1C
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Re: What does R stand for?

Postby Nicole Jacobs 1C » Tue Jan 16, 2018 8:34 pm

R should also be given on the formula and constant sheet Lavelle gives us for the test

Sarah Rutzick 1L
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Re: What does R stand for?

Postby Sarah Rutzick 1L » Tue Jan 16, 2018 8:53 pm

Going off of what everyone else said, there are several different gas constants so its important to use the one that ensures the correct units cancel out.

Adrian Lim 1G
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Re: What does R stand for?

Postby Adrian Lim 1G » Tue Jan 16, 2018 11:19 pm

Just to clarify, R is the ideal gas constant and its units are given per mole. Thus, when you are using this for q = mcdeltat, make sure the m is amount given in moles so the moles with the c would cancel.

Alejandra Rios 1L
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Re: What does R stand for?

Postby Alejandra Rios 1L » Thu Jan 18, 2018 3:25 pm

R is a constant which is used in ideal gas calculations. There are several values which you can use for R depending on what unit of pressure you are working with. These values will be given!

Juanyi Tan 2K
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Re: What does R stand for?

Postby Juanyi Tan 2K » Sat Jan 20, 2018 2:56 am

The one that we most commonly use in thermochemistry is R = 8.314 J·K-1·mol-1

Justin Folk 3I
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Re: What does R stand for?

Postby Justin Folk 3I » Sat Jan 20, 2018 10:54 am

Heat constant. When do you use 8.314 and when do you use 0.00821?

Cassandra Mullen 1E
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Re: What does R stand for?

Postby Cassandra Mullen 1E » Sat Jan 20, 2018 12:06 pm

Justin Folk 3I wrote:Heat constant. When do you use 8.314 and when do you use 0.00821?


Looking at the units helps you to determine which R to use. If you're using the ideal gas equation and pressure is in atm and volume is in L, then you would use 0.00821 Latm/molK. Homework problem 8.49 is an example of using the other R value, 8.314 J/Kmol.

Justin Folk 3I
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Re: What does R stand for?

Postby Justin Folk 3I » Fri Feb 16, 2018 5:16 pm

Yes, you're right sorry. THere's multiple R. You need to look at the units, on the third row of equation sheet. THanks

Jaewoo Jo 2L
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Re: What does R stand for?

Postby Jaewoo Jo 2L » Sun Feb 18, 2018 8:51 pm

I think until now, we've mostly seen the R values with atm or joules, and like what everyone said above, you just use the value with the units that cancel with corresponding units in your calculations.

Annie Lieu-1H
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Re: What does R stand for?

Postby Annie Lieu-1H » Mon Mar 12, 2018 8:56 am

The ideal gas constant! Like everyone said, make sure to look at the equations sheet and look at the right units to use for numbers in a particular problem.

Warda Sahib 2J
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Re: What does R stand for?

Postby Warda Sahib 2J » Thu Mar 15, 2018 6:44 pm

R is the ideal gas constant.


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