Why is Liter*atm equivalent to Joules?

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Discussion Overview

The discussion revolves around the equivalence of the units L*atm and Joules, particularly in the context of gas expansion and the work done by gases. Participants explore the conceptual understanding behind these units rather than relying solely on equations.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Patrick expresses confusion about why L*atm can be equivalent to Joules and seeks a conceptual explanation rather than a formulaic one.
  • One participant suggests confirming the consistency of units and relates L*atm to work done by a gas expanding at pressure.
  • Another participant provides a conversion factor (101.32 J = 1 L*atm) but questions the reasoning behind the gas expansion concept.
  • There is a discussion about the formula for work done by an expanding gas, expressed as PΔV, with some participants unsure about the underlying concepts.
  • Participants debate the nature of gas expansion, with one asserting that gas does not expand in a fixed volume, while another emphasizes the relationship between pressure, force, and volume in the context of work.
  • One participant seeks further clarification on how the formula W = PΔV connects to the definition of work and pressure.
  • A later reply attempts to guide Patrick through the reasoning behind the relationship between pressure, force, area, and displacement, ultimately leading to a better understanding of the concept.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the conceptual understanding of why L*atm is equivalent to Joules, and there are multiple competing views regarding the nature of gas expansion and the application of the work formula.

Contextual Notes

Some participants express uncertainty about the definitions and relationships involved in the concepts of work, pressure, and volume, indicating that further clarification may be needed to fully grasp the topic.

patrickbotros
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Hey forum! My name's Patrick. :biggrin:
I've been staring at this FOREVER, but I cannot seem to come up with an answer on my own. I've taken 1.5 semesters of physics, but I cannot figure this out. The reason I posted this in Chemistry is because I realized that the R constant can be written as 8.314 J/(mol*K) or as .0821 L*atm/(mol*K). So why is the Joule just a constant multiplier away from L*atm. I think my dilemma is that I cannot think of a SINGLE thing that would have the units L*atm. In your answers, please don't just draw up a formula that you think I should know and then verify that the units work out. I want a CONCEPT that verifies this, not an EQUATION.
Thanks so much in advance! I feel like this is the smartest website on the internet! #IwillNotMissYahooAnswers :smile:
 
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Hey Patrick. Welcome!

At the risk of being facetious, have you confirmed that the units are consistent? That, indeed, L*atm, when expressed in standard units, will be equivalent to Joules?

Then imagine a gas at some pressure (expressed in atm) expanding by some volume (in L). It seems reasonable to express the work done in units of L*atm. (Though I would stick with standard units.)
 
The conversion from L*atm to J is 101.32 J=1(l*atm). And I don't quite understand why that is reasonable, because I don't understand why I'm allowed to say that a gas is expanding. I think if you could sell me on this point then I would understand it: Why would the units of a gas expanding in some fixed volume be L*atm?
 
Do you agree that the work done by an expanding gas can be expressed as ##P\Delta V##?
 
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patrickbotros said:
gas expanding in some fixed volume

Gas doesn't expand in a fixed volume, gas expands changing volume. And it expands pushing things around apart.
 
Doc Al said:
Do you agree that the work done by an expanding gas can be expressed as ##P\Delta V##?
Hmmm. I'm not sure if I know why that is. I see that the units would work out:
Work=Force*ΔPosition, so Work=(Force/(unit area))*(ΔVolume)=Pressure*ΔVolume, right? It still seems a bit iffy, though. :H:frown::sorry: I don't know what concept says that W=PΔV, so if you could tell me a little more of what you know about that formula, I'd REALLY appreciate it. I know that work is area under the force vs. time curve, but I can't figure out how to connect that fact to pressure and volume.
Thanks so much for all your help!
 
What is the most basic definition of work (hint: it involves force and displacement)?

What is the definition of the pressure?

Imagine a piston moving in a cylinder. Assume the piston has a head surface A and is in contact with a gas of pressure P.

What is the force acting on the cylinder?

Now imagine this piston moved by L, compressing the gas. What was the work done?

What is A×L?
 
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Borek said:
What is the most basic definition of work (hint: it involves force and displacement)?

What is the definition of the pressure?

Imagine a piston moving in a cylinder. Assume the piston has a head surface A and is in contact with a gas of pressure P.

What is the force acting on the cylinder?

Now imagine this piston moved by L, compressing the gas. What was the work done?

What is A×L?
Hey THANKS! It took me a few minutes, but I totally get it! Pressure=Force/A, So Work=Pressure*A*L, Work=Pressure*∆V!
P.S. I like your hair.
 
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