R gas constant and kPa or Pa

[Isabel_Eslabon_2G]

I was going over the Sapling homework and problem #5 gives pressure in kPa.

What gas constant would we use when given that unit of pressure? Do we use 8.314 J/(K•mol)?
Also, why is the 8.314 J/(K•mol) the only value of R that doesn't have a unit of pressure in the units?

[BrittneyMyint1D]

There is a conversion on the constants sheet that says that 1 atm = 101.325 kPa, so I used this to convert the kPa to atm and used R = 8.206 * 10^-2 so the units would cancel out. The different values of gas constant R are basically the same, just in different units, which is why 8.314 does not have a pressure unit.

[Karl Yost 1L]

I would recommend converting kPa to atm and then using the gas constants that we are familiar with. Use the conversion: 1 atm = 101325 Pa.

[Immi Lee - 1D]

From my experience, I've only used 8.314 J/K*mol when I am solving for work/entropy, where the answer has units in Joules.

We use the 8.314 J/K*mol when we are working with certain equations, such as w = -RTln(V2/V1) where pressure is not involved in the equation. Another example would be the equations for entropy, deltaS = nRln(V2/V1) or deltaS = nRln(P1/P2) (For this second equation, the pressure is included but the units cancel out on their own). One helpful way to know which constant to use is to see what units you have, and what units need to be cancelled out in order get the units you need in your answer.

[Aditya Sundaram 3D]

Yup. Definitely try converting the pressure to atm before you start the problem to make everything more familiar and to make everything more standard.

[Alvin Lai 3J]

When give kPa, convert it to atm using 1 atm = 101.325 kPa. Then you can use the gas constant of R = 8.206 * 10^-2 L·atm·K-1·mol-1 to cancel out the atm and the other units. Hope this helps!

[Talia Dini - 3I]

If you are given the value of pressure in kPa, you can convert it into atm using the conversion 1 atm = 101.325 kPa. You can use the gas constant R = 8.206 *10^-2 L*atm*K^-1*mol^-1 so that the units would cancel out.

[Sophia Spungin 2E]

I would suggest converting kPa into atmospheres or another quantity for pressure that is listed as part of an R value. To determine what form to convert the pressure to, look at the units of the other quantities given (ie moles, liters, etc)

[Tatyana Bonnet 2H]

As others have stated, covert kPa to atm so that you can use R=8.206x10^-2 L Atm/K Mol. For other problems that give values other than the ones in the R gas constants try to find a way to convert them to fit the units in the constant.

[Jamie2002]

Just convert kPa to atm before proceeding with the problem, using 1 atm = 101.325 kPa.