PV=nRT units of R
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PV=nRT units of R
Hi, I'm working on a problem right now that uses the ideal gas law, and I was wondering about the units of R- sometimes I see different numbers used in different problems, so I am wondering if someone can explain to me the options for units for R and when to use them. Thanks!
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Re: PV=nRT units of R
Hi not necessarily sure if this is what you are asking but because you are usually solving for temperature, volume, pressure, or moles, you would base the units of are on the units of all your other constants. For example, if Pressure is in atm, volume is in L, and temperature is in Kelvin you would use L atm/mol/K. I hope this helps!
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Re: PV=nRT units of R
The numbers for R change depending on which units you are using. Depending on the question and which units it asks the answer to be in, you will have to use different forms of R in order to cancel out certain units to get the desired unit answers. I have attached a picture with all the different R values down below.
Re: PV=nRT units of R
Hi the value of R changes depending on the units that are being used for the pressure. For example, if your pressure is in atm, then R=8.206 x 10-2 L·atm*K^-1*mol^-1. If you used Torr then R=62.364 L·Torr·K^-1·mol^-1. If you want to convert between them, then you use the conversion factor (ie 1atm=760 torr). The units L*K^-1*mol^-1 are the same every time in R, but the unit, and therefore value, of the pressure will change the value of R. You can also reference them on the Constants_Equations Sheets in the Midterm section
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Re: PV=nRT units of R
The values for R change depending on which units you are using and the problem you are solving
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Re: PV=nRT units of R
Hi! If you look at the units in the problem, it should hint as to which value of R to use. I'm pretty sure that the textbook includes all of the possible values, but I've only really used 0.082 or 8.314 in word problems. I hope this helps!
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Re: PV=nRT units of R
Hello! The R value, 0.08206, is going to be used in the equation PV=nRT, as it cancels out units better. The R value 8.314 will be used when the question is asking for work, Gibbs free energy, or entropy, etc, as it cancels out units better.
Hope this helps!
Hope this helps!
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Re: PV=nRT units of R
For R, the two main values we use in class is 8.314 J/K/Mol and 0.08206 L/atm.
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Re: PV=nRT units of R
The way I know which R to use is simply by looking at the units given in the problem. I think of it like solving a puzzle and figuring out what pieces are needed. If the question give you Liters, then you use the R that includes Liters (so then it can cancel out). Basically whatever can be cancelled out is the R you use.
Re: PV=nRT units of R
You have to pick R based on what units your other variables (ie: PVnT) are. Let's say the volume was in liters then you should pick the R which has liters, so that it will cancel out. So you are just picking it based on what you need to cancel out in order to solve the problem.
Re: PV=nRT units of R
The main R values that will be used would be or . Just see which values are being used and choose accordingly, for example if the equation gives an answer in Joules you use 8.314 or if you are given Litres and atmospheres you use 0.08206.
An easy way to convert between them is given on our sheet, multiply 0.08206 by 101.325 (used to convert between Litre-atmospheres to Joules).
An easy way to convert between them is given on our sheet, multiply 0.08206 by 101.325 (used to convert between Litre-atmospheres to Joules).
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Re: PV=nRT units of R
Hi
In addition to the other responses, I have found that actually writing out the units for each term and making sure they cancel out really help me not only for picking the right r value for each problem but also to make sure I don't make a silly units mistake like using j instead of kj or celsius instead of k.
In addition to the other responses, I have found that actually writing out the units for each term and making sure they cancel out really help me not only for picking the right r value for each problem but also to make sure I don't make a silly units mistake like using j instead of kj or celsius instead of k.
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Re: PV=nRT units of R
In the equation sheet, we are given three values for R which are R= 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. For the last two values, these include pressure(atm or bar) and volume(L). Therefore, it depends on the other known values that you know since if they give you the volume and the pressure in atm, it would be better to use the 2nd value of 8.206 x 10^-2. Something that helps me out is writing out the units in order to make sure that I end up with the units that I want and everything else is canceled.
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Re: PV=nRT units of R
The value of R that you should use depends on the units of pressure that you are given. If pressure is given in ATM, you use 0.08206, but if pressure if given in J*K^-1, you use 8.314; units must be kept consistent throughout the calculation.
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