## Units for Pressure

$PV=nRT$

Emma Edmond 3E
Posts: 29
Joined: Fri Sep 25, 2015 3:00 am

### Units for Pressure

When calculating for pressure, or using pressure in the ideal gas equation, should we always convert to pascals or can be leave it in the form of bar or atm?

Sara Kashani 4j
Posts: 9
Joined: Fri Sep 25, 2015 3:00 am

### Re: Units for Pressure

For idea gas law, the unit of pressure must be in atm.

zhajee
Posts: 23
Joined: Fri Sep 25, 2015 3:00 am

### Re: Units for Pressure

This cancels out the atm unit in R, which is .0821 L * atm/mol *K

Claire Malley 2B
Posts: 23
Joined: Fri Sep 25, 2015 3:00 am

### Re: Units for Pressure

You can use either bar or atm, pascals are not preferred because they do not have a gas constant like atm or bar, which are .08206 L.atm.K(-1).mol(-1) and .08314 L.bar.K(-1).mol(-1), respectively.

Victor Qiu 1C
Posts: 106
Joined: Wed Sep 30, 2020 9:59 pm
Been upvoted: 2 times

### Re: Units for Pressure

I don't think the unit of pressure should must be in atm. I think just using same units in calculation would be fine.
R=8.314 J mol-1 K-1=0.08205 L atm mol-1 K-1=62.363 mmHg L mol-1 K-1

Kathy_Li_1H
Posts: 90
Joined: Wed Sep 30, 2020 9:31 pm

### Re: Units for Pressure

Hi! I believe because the Standard unit for pressure is atm, we usually have to leave most answers units of atm.

Kyla Roche 2K
Posts: 93
Joined: Wed Sep 30, 2020 9:59 pm

### Re: Units for Pressure

I recall hearing that 1 bar and 1 atm are essentially the same, therefore they are interchangeable, but that we will use atm.

Gabe_Ek 1G
Posts: 93
Joined: Wed Sep 30, 2020 10:04 pm

### Re: Units for Pressure

Is there any case where we won't use atm? Such as having to change the final answer into Pa (Pascal) or kPa?

Austin Aldujaili 2D
Posts: 91
Joined: Wed Sep 30, 2020 9:46 pm

### Re: Units for Pressure

I wouldn't think that there would be any situation where we need to convert to Pascals since Lavelle didn't talk about that unit at all. I think its important to just read the question and figure out what units they want their final answer in.

Brian Nguyen 2I
Posts: 91
Joined: Wed Sep 30, 2020 9:49 pm

### Re: Units for Pressure

Don't convert to pascals. We use atm or barr in these problems involving pressure, so there is no need for conversion.

Posts: 80
Joined: Wed Sep 30, 2020 9:48 pm

### Re: Units for Pressure

So do we ever need to convert to pascals or will it always be in atm.

Andy Hernandez
Posts: 56
Joined: Wed Sep 30, 2020 9:50 pm

### Re: Units for Pressure

the unit of pressure should be in atm

Kelly Ha 1K
Posts: 93
Joined: Wed Sep 30, 2020 9:52 pm
Been upvoted: 1 time

### Re: Units for Pressure

Maddie Turk Disc 2C wrote:So do we ever need to convert to pascals or will it always be in atm.

I don't think we will have to convert to pascals since Dr. Lavelle hasn't mentioned it yet. We will most likely be given atm or bar units for pressure.

josephspindler2H
Posts: 92
Joined: Wed Sep 30, 2020 9:54 pm
Been upvoted: 1 time

### Re: Units for Pressure

We will be using atm. As Dr. Lavelle stated in lecture, 1 bar is very close to 1 atm, so for our purposes we can just use atm.

Posts: 94
Joined: Wed Sep 30, 2020 9:40 pm

### Re: Units for Pressure

We usually use atm for units as it is part of the SI system. Bar is not, and so we usually convert bar to atm unless the problem asks us to use bar specifically.

AndrewNguyen_2H
Posts: 90
Joined: Wed Sep 30, 2020 9:59 pm

### Re: Units for Pressure

The constant uses atm so use atm to make sure the units cancel nicely.

Shivani Kapur 2J
Posts: 95
Joined: Wed Sep 30, 2020 9:59 pm

### Re: Units for Pressure

I believe we will mostly be using atm for the extent of this class.

Naomi Hernandez-Ramirez 1J
Posts: 45
Joined: Wed Feb 19, 2020 12:17 am

### Re: Units for Pressure

like most I agree that the standard unit for pressure = atm, I know you've been getting Atm and bar, but I think atm is the correct unit

Linette Choi 3L
Posts: 93
Joined: Wed Sep 30, 2020 9:51 pm

### Re: Units for Pressure

Along with everyone else I believe it should be in atm, however, it could vary on what units the question asks you to convert to.

Keshav Patel 14B 2B
Posts: 94
Joined: Wed Sep 30, 2020 9:40 pm

### Re: Units for Pressure

Professor Lavelle said to use the atm for pressure. He said that it’s not too different and he prefers atm since it’s been around longer.

Queena Chu 3E
Posts: 86
Joined: Wed Sep 30, 2020 10:09 pm

### Re: Units for Pressure

Hi! The unit should be atm.

Melanie Lin 3E
Posts: 90
Joined: Wed Sep 30, 2020 9:38 pm

### Re: Units for Pressure

I usually convert to atm because of the given R constant (that uses atm). Since it will probably be given on the constants sheet, it'll be helpful converting to atm.

Diana Aguilar 3H
Posts: 90
Joined: Wed Sep 30, 2020 9:50 pm

### Re: Units for Pressure

Hi! I believe the unit should be atm, I do not think we have to convert to pascals.

nayha a 1E
Posts: 96
Joined: Wed Sep 30, 2020 9:54 pm

### Re: Units for Pressure

Hi! I believe we will be using atm (:

Jose Miguel Conste 3H
Posts: 91
Joined: Sat Oct 03, 2020 12:15 am

### Re: Units for Pressure

I believe it is with respect to the problem and what units they give, sometimes it can give mmHg or atm or torr, but take it with a grain of salt, you should ask a TA this question

Posts: 78
Joined: Wed Sep 30, 2020 9:34 pm

### Re: Units for Pressure

Hello! I agree with the previous posts. We need to use atm so the units cancel out properly.

Lily Mohtashami
Posts: 142
Joined: Wed Sep 30, 2020 9:34 pm

### Re: Units for Pressure

I agree, I think because Lavelle has only used atm we should be using atm as the units for pressure unless we learn otherwise.

Joshua_Chan_3K
Posts: 36
Joined: Wed Nov 18, 2020 12:27 am

### Re: Units for Pressure

Its probably best to leave it in ATM right now or for possibly the entire class but really each one of them has its own R value in the ideal gas law which you can search up or calculate just using the conversion factor (Although that method kinda takes away the whole point of leaving it in another unit). Just make sure not to use the wrong unit with the wrong R value and convert at the end to the unit the question is asking for.

Anthony_Sandoval_1D
Posts: 91
Joined: Wed Feb 19, 2020 12:15 am

### Re: Units for Pressure

It is in my opinion that we will be using atm in this specific class.

Brandon Le 3C
Posts: 89
Joined: Wed Sep 30, 2020 9:49 pm

### Re: Units for Pressure

Generally, atm is the most commonly used unit when it comes to these kinds of problems. But there are different values of R in the ideal gas equation that would accommodate for different units of pressure.

Rayna Irving 2C
Posts: 93
Joined: Wed Sep 30, 2020 9:33 pm

### Re: Units for Pressure

I'm pretty sure we use atm because its units line up with the R value we are given on the equation sheet so the units can cancel, but in the lecture he said that 1 atm is also pretty close to 1 bar if you're wondering.

Muskaan Abdul-Sattar
Posts: 79
Joined: Wed Nov 13, 2019 12:19 am

### Re: Units for Pressure

I believe units of pressure should be in atm.

Teti Omilana 1G
Posts: 82
Joined: Wed Sep 30, 2020 10:05 pm

### Re: Units for Pressure

Units were left in atm based off of Lavelle's examples.

Sam Wentzel 1F 14B
Posts: 129
Joined: Wed Sep 30, 2020 9:50 pm
Been upvoted: 1 time

### Re: Units for Pressure

Convert to ATM, so that the units cancel when plugging into the equation. Hope this helps!

Caelin Brenninkmeijer 1G
Posts: 90
Joined: Wed Sep 30, 2020 9:50 pm

### Re: Units for Pressure

Pressure units should be in atm!

Ariel Guan 1H
Posts: 97
Joined: Wed Sep 30, 2020 9:36 pm
Been upvoted: 1 time

### Re: Units for Pressure

i think pressure should be in atm

Keeryth Sandhu 1H
Posts: 97
Joined: Wed Sep 30, 2020 10:04 pm

### Re: Units for Pressure

I believe for ideal gas law it should be in atm

emwoodc
Posts: 81
Joined: Fri Aug 09, 2019 12:16 am

### Re: Units for Pressure

Dr. Lavelle said that bar is technically the correct unit but since atm is so close to bar you can use atm!

Sable Summerfield
Posts: 33
Joined: Tue Nov 17, 2020 12:18 am

### Re: Units for Pressure

What is the difference between Barr and Atm? Why are they interchangeable?

Susan Chamling 1F
Posts: 91
Joined: Wed Sep 30, 2020 9:42 pm

### Re: Units for Pressure

I think from examples in lecture atm tends to be used more often

Karen Zheng_2K
Posts: 88
Joined: Fri Sep 29, 2017 7:04 am

### Re: Units for Pressure

From Andrew's discussion section he said that we can use either bars or atm, but if something is in Pascals, you would need to convert it back to atm usually!

Megan Sparrow 1A
Posts: 110
Joined: Wed Sep 30, 2020 9:49 pm
Been upvoted: 4 times

### Re: Units for Pressure

Okay, thank you for letting us know! Does anyone know if for the test if we are expected to know how to convert from Barr to atm or atm to pascals? I'm not sure if it was mentioned in the section outline or if this was just for practice on the homework and such.