## Constant R

Haley Dveirin 1E
Posts: 101
Joined: Sat Jul 20, 2019 12:17 am

### Constant R

When do you use the constant R=8.314 vs 8.206x10^-2 and what are the units for each

Jessica Booth 2F
Posts: 101
Joined: Fri Aug 30, 2019 12:18 am

### Re: Constant R

When do you use the constant R=8.314 vs 8.206x10^-2 and what are the units for each
The units are R = 8.314 J/(K mol) and 8.206x10^-2 L atm/(K mol). You use 8.314 whenever you are working with J and you use 8.206x10^-2 when using atm and L.

JesseAuLec1Dis1G
Posts: 52
Joined: Mon Jun 17, 2019 7:23 am

### Re: Constant R

You just have to pay attention to the units of each. Just make sure your calculations cancel out units so you end up with the units you want when you've finished all of your calculations.

Natalie Benitez 1E
Posts: 100
Joined: Fri Aug 02, 2019 12:15 am

### Re: Constant R

What circumstances should we use the difference values of R?

Benjamin Feng 1B
Posts: 102
Joined: Sat Sep 07, 2019 12:19 am

### Re: Constant R

Usually when you are solving for pressure or volume using PV=nrt you use the one with liters and atm (.08205). If you are solving for work, it is more common to use the one with Joules in the units (8.3145).

MAC 4G
Posts: 121
Joined: Wed Sep 18, 2019 12:16 am

### Re: Constant R

Natalie Benitez 1E wrote:What circumstances should we use the difference values of R?

The best way to figure out which value of R to use, I would look at what units you're given from the question to see what you can cancel out. Similarly, you can also look at what units you need in your final answer as to what you are looking for to determine how the units will cancel out to give you your desired units.

For example, if you are looking for an answer in joules, and you are given temperature (in K) and moles (or a value you can convert to these units) you would use R = 8.314 J/(K mol). So, the K and moles will cancel out leaving you with Joules.

Brian J Cheng 1I
Posts: 115
Joined: Thu Jul 11, 2019 12:15 am

### Re: Constant R

As many have said, look at the units you need for a certain calculation and choose the R value accordingly. For example: you're given values in Liters, pressure, temperature, and mols, then you would use R = 0.08206 L*atm/K*mol

pmokh14B
Posts: 107
Joined: Sat Aug 17, 2019 12:15 am

### Re: Constant R

The units for each are on the equation sheet. Depending on that you decide which to use.

Kishan Shah 2G
Posts: 132
Joined: Thu Jul 11, 2019 12:15 am

### Re: Constant R

The best way to determine when to use which instead of memorizing them is to look at the units to see which units you are working with and what you want to end up with.

Emil Velasco 1H
Posts: 96
Joined: Wed Nov 21, 2018 12:19 am

### Re: Constant R

You can find the units used on the equation sheet

Just look for what units the problem gives you and what you are trying to get. Using R with the right units allows you to cancel out the things you don't need in order to get what you want

305421980
Posts: 101
Joined: Sat Sep 07, 2019 12:16 am

### Re: Constant R

To determine which version of R is used I always look at what other units are being used in the problem and which correspond to the R constant units on the equation sheet.

EllieSchmidtke_4I
Posts: 51
Joined: Wed Feb 20, 2019 12:16 am

### Re: Constant R

Which version of the gas constant (R) applies to your equation depends on the units present in the equation.

Juana Abana 1G
Posts: 100
Joined: Wed Sep 18, 2019 12:15 am

### Re: Constant R

To determine when to use which it is best to look at the units to see which units will cancel out and also see what units you will be left with.

Jack Riley 4f
Posts: 100
Joined: Sat Aug 24, 2019 12:17 am

### Re: Constant R

Just look at the units needed in the problem and choose the R with those units same units

Esha Chawla 2E
Posts: 108
Joined: Thu Jul 25, 2019 12:17 am

### Re: Constant R

Haley Dveirin 1E wrote:When do you use the constant R=8.314 vs 8.206x10^-2 and what are the units for each

To determine which R to use, look at the units provided in the problem. The units for R=8.314 are J/K*mol and the units for R = 0.08206 are L*atm/K*mol.

Aarushi Solanki 4F
Posts: 107
Joined: Sat Jul 20, 2019 12:17 am

### Re: Constant R

You use 8.314 when the units are J/(mol*K). You use 0.08206 when the units are (atm*L)/(mol*K).