Which R to use?
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Which R to use?
With the different values for R available for the PV=nRT equation, how do we know which one to use for different problems?
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Re: Which R to use?
I think that it is based off the units in the problem? Like the units of the other variables and what units the question wants can influence what value of R you use.
Re: Which R to use?
Yeah I would use the R value with units that correspond to units used in the problem. Not 100% sure though, ask your TA.
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Re: Which R to use?
Hi! It should largely depend on what units you are dealing with, like atm, torr, etc.
Re: Which R to use?
You should use the R that correspond to the units in the question. I found myself using R = 8.314 x 10^-2 L.bar.K^-1.mol^-1 when going through the achieve textbook questions though.
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Re: Which R to use?
The R that you use is relative to the units used in the problem, so its not constant but changes depending on the question :)
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Re: Which R to use?
For the equation PV=nRT, R is the gas constant: 8.314 J/(mol)(K). If the given units in the problem are not in SI units, the value may vary.
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Re: Which R to use?
I would use the R value with units that match those in the problem you are solving.
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Re: Which R to use?
Does anyone know in what cases you would use the R constant of 8.314 J*K^-1*mol^-1? For the other 2 constants the units that measure partial pressure are included (atm and bar). Can joules be used to measure pressure?
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Re: Which R to use?
Each value has different units, so I'd use the value that corresponds with the units of the problem given!
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Re: Which R to use?
Look at the units you are using in the formula, and pick the R constant with the correct units. Remember, in the end you want all your units to cancel out.
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Re: Which R to use?
I was confused about this too, but apparently you use whatever units you were given in the problem.
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Re: Which R to use?
Hi!
With the different units used in the Ideal Gas Law, the value of R depends on the question.
The most common value for R = 8.314 J/Kmol but 8.206E-2 Latm/Kmol and 62.364 LTorr/Kmol are also used.
I hope this helps!
With the different units used in the Ideal Gas Law, the value of R depends on the question.
The most common value for R = 8.314 J/Kmol but 8.206E-2 Latm/Kmol and 62.364 LTorr/Kmol are also used.
I hope this helps!
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Re: Which R to use?
The R used is dependent on units. The values are the same with respect to their units. 8.314 is the most commonly used one since it’s units are J/kmol
Re: Which R to use?
Depending on the units of your values, a different numerical value of R should be used. R= 8.314 J/mol*K is most common.
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Re: Which R to use?
305561744 wrote:Does anyone have a sheet that lists the different Rs with their units?
The sheet is called Constants and Equations and is on the Chem 14B section of lavelle's website.
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Re: Which R to use?
Depending on what units you are given for a specific problem, the R value will be different.
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Re: Which R to use?
The value for R that you choose is dependent on the units given for the problem!
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Re: Which R to use?
The R value that you end up using depends on the units used in the problem, but once you get in the habit of doing problems, you kind of figure out which R to use when because of the typical units of that problem.
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Re: Which R to use?
Choosing which R to use depends completely on the units in the equation. For pv=nRT we always use R=.08206 atm x L / m x K because of how its units fit into the equation. Hope this helps!
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Re: Which R to use?
The R you use will depend on the units given to you. For example if pressure was given in pascals you would use the 8.31 R constant so that pascals can cancel.
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Re: Which R to use?
Hi! I agree with everyone else, I think a visual would help. I refer to this chart, taking into account the rest of units of measurements.
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Re: Which R to use?
Hey! You would use the different values of R corresponding to the units of the other values in the expression
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Re: Which R to use?
For all the equations using energy, use 8.314. The only equation that uses R = 0.08 that I can immediately think of is PV = nRT. Just, when in doubt, check the units of the problem.
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