Which R value to choose

[emmaferry2D]

when using equations like deltaU=deltaH =PdeltaV I'm confused on which R constant to plug in when trying to solve for PdeltaV using the ideal gas law equation

[Megan Chan 3A]

I think the best way to determine which R value to use is to look at the units and find the one that will cancel to give you the units you need for your final answer. In the case for the ideal gas law, PV = nRT, you would choose 0.08206 L.atm.K^-1.mol^-1 since these are the units for pressure, volume, moles, and temperature. The other value, 8.314 J.K^-1.mol^-1, wouldn't make sense since there are no joules in the ideal gas law.

[KhanTran3K]

hey, with choosing the correct R-value, it is important to look at the units and the context of the question. One R value relates to energy while one is related to the ideal gas law. When using PV=nRT, we would use the .0821 value, since this relates it to Lxatm/Kxmol in order to cancel. When relating it to energy, we have 8.314 J/Kxmol.

[Brianna Martilla 1C]

They each have their own units being used so they are each applicable to their own problems. I had a hard time differentiating the two for a bit until I paid attention to the units.

[Jamie2002]

If you are trying to find the mols of gas using PV = nRT, use R= 0.08206 L (atm)/ (mol (K)). The units will cancel out and you will be able to find the number of mols.

[Nathan Lao 2I]

Like most questions, it really depends on the units given. Technically they are all interchangeable but it's best to use the R value that corresponds with the units given in the problem. This would make it the easiest in terms of calculations. For example, if you're trying to find the entropy change of 1.00L of gas at 298K has a pressure of 1.00 atm, you would use 0.08206 (L.atm)/(mol K) as the R constant.

[Griffin G]

Honestly whenever you aren't sure which constant to use, always refer to the units and find the one that will give you the proper units in the end.

[Lauren Mungo 1K]

It is always best to look at the units of the problem because you are going to need to pick the R value that corresponds with the units!

[Karen Zheng_2K]

Units help in determining which R value to use!

[Gian Boco 2G]

I try my best to keep track of the units im given and then match them to the R constant accordingly so the calculation produces the units I want.

[Carolina Gomez 2G]

The R you use should be consistent with the units. Keep track of the units throughout the problem to make sure, you are using the correct R.

[Sreeram Kurada 3H]

You typically use the R-value in terms of joules so like 8.314. But like other people are saying, it really depends on what you are solving for.

[Anastasia Yulo 1C]

To help decide which R to use, I am always wary of the units at play. For PV=nRT it would make the most sense to use R = 0.08206 L.atm.K^-1.mol^-1

[Diana Aguilar 3H]

When trying to choose what R value to use, you should try looking at/keeping track of the units given to you in the problem to ensure that the units all match so that in your final answer, you end up with the desirable units.