Units for Pressure


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Emma Edmond 3E
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Units for Pressure

Postby Emma Edmond 3E » Fri Nov 13, 2015 10:46 am

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
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Re: Units for Pressure

Postby Sara Kashani 4j » Fri Nov 13, 2015 11:05 am

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

zhajee
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Re: Units for Pressure

Postby zhajee » Fri Nov 13, 2015 5:20 pm

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

Claire Malley 2B
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Re: Units for Pressure

Postby Claire Malley 2B » Sat Nov 14, 2015 9:50 am

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
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Re: Units for Pressure

Postby Victor Qiu 1C » Sun Jan 10, 2021 7:58 am

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
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Re: Units for Pressure

Postby Kathy_Li_1H » Sun Jan 10, 2021 10:14 am

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

Kyla Roche 2K
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Re: Units for Pressure

Postby Kyla Roche 2K » Sun Jan 10, 2021 10:18 am

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
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Re: Units for Pressure

Postby Gabe_Ek 1G » Sun Jan 10, 2021 12:05 pm

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
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Re: Units for Pressure

Postby Austin Aldujaili 2D » Sun Jan 10, 2021 12:11 pm

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
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Re: Units for Pressure

Postby Brian Nguyen 2I » Sun Jan 10, 2021 6:46 pm

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

Maddie Turk Disc 2J
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Re: Units for Pressure

Postby Maddie Turk Disc 2J » Sun Jan 10, 2021 6:55 pm

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

Andy Hernandez
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Re: Units for Pressure

Postby Andy Hernandez » Sun Jan 10, 2021 6:56 pm

the unit of pressure should be in atm

Kelly Ha 1K
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Re: Units for Pressure

Postby Kelly Ha 1K » Sun Jan 10, 2021 6:57 pm

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
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Re: Units for Pressure

Postby josephspindler2H » Sun Jan 10, 2021 7:17 pm

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.

Adrienne Chan 1G
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Re: Units for Pressure

Postby Adrienne Chan 1G » Sun Jan 10, 2021 8:02 pm

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
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Re: Units for Pressure

Postby AndrewNguyen_2H » Sun Jan 10, 2021 8:03 pm

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

Shivani Kapur 2J
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Re: Units for Pressure

Postby Shivani Kapur 2J » Sun Jan 10, 2021 8:20 pm

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

Naomi Hernandez-Ramirez 1J
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Re: Units for Pressure

Postby Naomi Hernandez-Ramirez 1J » Sun Jan 10, 2021 8:23 pm

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
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Re: Units for Pressure

Postby Linette Choi 3L » Sun Jan 10, 2021 8:26 pm

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
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Re: Units for Pressure

Postby Keshav Patel 14B 2B » Sun Jan 10, 2021 8:34 pm

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
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Re: Units for Pressure

Postby Queena Chu 3E » Sun Jan 10, 2021 8:45 pm

Hi! The unit should be atm.

Melanie Lin 3E
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Re: Units for Pressure

Postby Melanie Lin 3E » Sun Jan 10, 2021 8:51 pm

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
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Re: Units for Pressure

Postby Diana Aguilar 3H » Sun Jan 10, 2021 8:55 pm

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

nayha a 1E
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Re: Units for Pressure

Postby nayha a 1E » Sun Jan 10, 2021 8:56 pm

Hi! I believe we will be using atm (:

Jose Miguel Conste 3H
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Re: Units for Pressure

Postby Jose Miguel Conste 3H » Sun Jan 10, 2021 9:12 pm

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

LarisaAssadourian2K
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Re: Units for Pressure

Postby LarisaAssadourian2K » Sun Jan 10, 2021 9:16 pm

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

Lily Mohtashami
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Re: Units for Pressure

Postby Lily Mohtashami » Sun Jan 10, 2021 9:26 pm

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
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Re: Units for Pressure

Postby Joshua_Chan_3K » Sun Jan 10, 2021 10:30 pm

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
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Re: Units for Pressure

Postby Anthony_Sandoval_1D » Sun Jan 10, 2021 11:09 pm

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

Brandon Le 3C
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Re: Units for Pressure

Postby Brandon Le 3C » Sun Jan 10, 2021 11:15 pm

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
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Re: Units for Pressure

Postby Rayna Irving 2C » Sun Jan 10, 2021 11:21 pm

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
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Re: Units for Pressure

Postby Muskaan Abdul-Sattar » Sun Jan 10, 2021 11:48 pm

I believe units of pressure should be in atm.

Teti Omilana 1G
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Re: Units for Pressure

Postby Teti Omilana 1G » Sun Jan 10, 2021 11:50 pm

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

Sam Wentzel 1F 14B
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Re: Units for Pressure

Postby Sam Wentzel 1F 14B » Sun Jan 10, 2021 11:57 pm

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

Caelin Brenninkmeijer 1G
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Re: Units for Pressure

Postby Caelin Brenninkmeijer 1G » Sun Jan 10, 2021 11:59 pm

Pressure units should be in atm!

Ariel Guan 1H
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Re: Units for Pressure

Postby Ariel Guan 1H » Mon Jan 11, 2021 6:35 pm

i think pressure should be in atm

Keeryth Sandhu 1H
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Re: Units for Pressure

Postby Keeryth Sandhu 1H » Mon Jan 11, 2021 6:38 pm

I believe for ideal gas law it should be in atm

emwoodc
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Re: Units for Pressure

Postby emwoodc » Tue Jan 12, 2021 12:10 am

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

Sable Summerfield
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Re: Units for Pressure

Postby Sable Summerfield » Sun Jan 17, 2021 10:49 pm

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

Susan Chamling 1F
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Re: Units for Pressure

Postby Susan Chamling 1F » Mon Jan 18, 2021 1:46 am

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

Karen Zheng_2K
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Re: Units for Pressure

Postby Karen Zheng_2K » Mon Jan 18, 2021 8:39 am

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
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Re: Units for Pressure

Postby Megan Sparrow 1A » Mon Jan 18, 2021 8:44 am

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.


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