R constant of an Ideal Gas

[Bronson Mathos 1H]

Hello, I found myself a bit lost on the Sapling homework when working on work equations as I was always unsure of which R constant to insert for the Ideal Gas Law, and I was wondering if someone could explain how to know which R value to use when solving these questions.

[Sophia Stewart 3F]

I'd recommend writing out the units of everything in the equation you are using. For example, write out that n is in moles, that temperature is in K (or *C).. and so on. Then from that, consult the equation sheet and look at which R value has units that match the others in the equation and would therefore cancel them out.

[Kyle_Lee_2B]

when using the r constant you need to know what you are working with. For instance, you would need to use the r constant of 8.314472 L*pKa/k*mol in pv=nrt, if your p value is using pKa rather than atm. look at the surrounding units in the equation and make sure that the r constant is either getting rid of or adding the correct unit when you reach your answer.

[Kelly Ha 1K]

I definitely had this problem at first too! Basically just always check your units; make sure the correct units cancel out to leave you with your desired value. It helps to write out all the units of the values when calculating so you can double check you picked the right R to use.

[Alejandro Gonzalez 2G]

I usually try to look at the units in order to see which R constant to use (atm vs J).

[Eileen Quach Dis 2A]

On the equation sheet, looking at the multiple possible values for R, you can look at what units are being used and plug that into whatever problem you're solving to see if the units cancel.

[Kyle_Lee_2B]

when you are writing the equation, practice writing all the units. this way you can know what unit you need to find, for instance, V will be L and P will be atm, so your answer must have the unit you are solving for, nothing more nothing less. The different R values have diff units so as long as your units are canceling when you need them to cancel and you end up with the end unit, that was the correct r value.

[Darlene Lien 3E]

I also agree with the above comments! I just use the ones that would cancel out the units.

[Samir 3I]

This is why it is important and very helpful to write out the units for every value you are using in an equation. Personally, I like to plug in all of the values (with units) that I know into the equation I am using and save the gas constant (R) for last. Then I look at my equations sheets and find which variation of the gas constant will cancel out the units I see in my written out equation.

[Crystal Pan 2G]

You will typically use the gas constant according to what is given in the problem. You want to cancel out units that are not in the final answer.

[Madeline Ogden 3B]

I agree with the other comments! Typically, the first unit I try to look for is liters and atm, as this is a way of telling you that you have to use 0.08206 instead of 8.314 since these two units typically cancel out. Hope this helps!

[Tiao Tan 3C]

I usually pay attention to the units given in the question and the units the answer want us to use. If the question gives volume in liters and pressure in atm, then I would use the R constant that has units L and atm. If the questions further asks for joules, remember to convert your answer in L*atm to J.

[Michelle Nguyen 3F]

Write out the units of the problem from the given measurements or data recorded! Depending on which units you have, you can use the right R for the problem :)

[Evonne Hsu 1J]

Pay attention to the units indicated in the question and you can determine which R to use (R for LatmJ/cal/torr/etc).

[Nan_Guan_1L]

Basically what matters is the unit of R. So you would want to take a look at the units you have got and the unit you want to end up with. Usually R could fix the difference between the units and you would just select the R value with the proper units.

[Jeremy Wei 2C]

Hi! For me I would look at the units for the R constants given and see which R value's units best fit the equation you are using.

[Kathy_Li_1H]

Hi! For me what's worked best has been just looking at what units you need for the end result and adjusting accordingly.