R constant for PV=nRT


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Jessica Castellanos
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R constant for PV=nRT

Postby Jessica Castellanos » Mon Jan 20, 2020 11:17 am

What is the the value of R in PV=nRT? I've seen two different values and don't know which is which.

Kevin Antony 2B
Posts: 99
Joined: Sat Sep 07, 2019 12:16 am

Re: R constant for PV=nRT

Postby Kevin Antony 2B » Mon Jan 20, 2020 11:20 am

R is equal to 8.3145 x 10^-2

sarahforman_Dis2I
Posts: 109
Joined: Sat Aug 17, 2019 12:18 am

Re: R constant for PV=nRT

Postby sarahforman_Dis2I » Mon Jan 20, 2020 12:27 pm

Jessica Castellanos wrote:What is the the value of R in PV=nRT? I've seen two different values and don't know which is which.


Yes, you are correct that there are two values for R. The difference between these values are the units that are used. This means that you need to be very careful when you are using the ideal gas law in order to make sure that you are using the correct units.
For example, R= 8.314 J/(Kmol) and .008206 L(atm)/(Kmol) and 0.008314 L(bar)/(Kmol) and 62 L(Torr)/(Kmol).

Use the gas constant that will cancel with the units that you were given in the problem. For example, if you were given pressure in atm, use .008206 L(atm)/(Kmol). If you were given a pressure in Pa (which you could easily convert to Bars) use 0.008314 L(bar)/(Kmol)

Amy Kumar 1I
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Joined: Thu Jul 11, 2019 12:15 am

Re: R constant for PV=nRT

Postby Amy Kumar 1I » Mon Jan 20, 2020 1:51 pm

The R values are constant and change based on the units of pressure being used.

Kallista McCarty 1C
Posts: 212
Joined: Wed Sep 18, 2019 12:18 am

Re: R constant for PV=nRT

Postby Kallista McCarty 1C » Mon Jan 20, 2020 3:19 pm

The R value will be given on the constant and equations sheet on the test! I know that there are different units that you use depending on the question, but they will both be given

205405339
Posts: 77
Joined: Thu Jul 11, 2019 12:16 am

Re: R constant for PV=nRT

Postby 205405339 » Mon Jan 20, 2020 3:33 pm

R can have different values depending on what units are needed for the equation

Robin Cadd 1D
Posts: 113
Joined: Thu Jul 11, 2019 12:16 am

Re: R constant for PV=nRT

Postby Robin Cadd 1D » Mon Jan 20, 2020 3:48 pm

Look at the units of pressure to differentiate between the R constants. Whichever R constant contains the same units of pressure as the data you have is the one you should choose to make further calculations.

Eunice Nguyen 4I
Posts: 100
Joined: Sat Aug 17, 2019 12:17 am

Re: R constant for PV=nRT

Postby Eunice Nguyen 4I » Mon Jan 20, 2020 3:49 pm

R value is a constant and is chosen based on which unit is given in the problem. Make sure to keep an eye out for the unit so that you know which R value to use!


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