Why is Liter*atm equivalent to Joules?

In summary, the conversation discusses the relationship between the R constant and the units of Joules and L*atm. The concept of work done by an expanding gas is introduced and explained using the formula W=PΔV. The conversation also touches on the definitions of work and pressure, and how they relate to the concept of work done by a gas. The conversation concludes with the realization that Work=Pressure*∆V.
  • #1
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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  • #2
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.)
 
  • #3
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?
 
  • #4
Do you agree that the work done by an expanding gas can be expressed as ##P\Delta V##?
 
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  • #5
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.
 
  • #6
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!
 
  • #7
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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  • #8
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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1. Why is Liter*atm equivalent to Joules?

The concept of Liter*atm being equivalent to Joules is rooted in the understanding of energy and its different forms. In the International System of Units (SI), energy is measured in Joules (J), which is a unit of work or heat. One Joule is equal to the work done by a force of one newton acting through a distance of one meter. On the other hand, Liter*atm is a unit of energy used in thermodynamics, specifically in the calculation of work. It is equivalent to 101.325 Joules.

2. How is the Liter*atm value derived?

The value of Liter*atm is derived from the ideal gas law, which states that the product of pressure and volume is proportional to the absolute temperature of a gas. By converting the units of pressure (atm) and volume (Liters) to SI units and using the ideal gas constant, the value of Liter*atm is calculated to be 101.325 Joules.

3. Is Liter*atm only used in thermodynamics?

Liter*atm is primarily used in thermodynamics to calculate work, but it can also be used in other fields that involve energy conversions and calculations. For example, it can be used in the study of fuel efficiency in vehicles, as well as in the measurement of energy released in chemical reactions.

4. Can Liter*atm be converted to other units of energy?

Yes, Liter*atm can be converted to other units of energy such as Joules, calories, and electronvolts. The conversion factor between Liter*atm and Joules is 101.325 J, while the conversion factor to calories is 2.389x10^4 cal. These conversions are useful in making energy calculations and comparisons across different systems and units.

5. Why is it important to understand the equivalence of Liter*atm and Joules?

Understanding the equivalence of Liter*atm and Joules is important because it allows for the conversion and comparison of energy units in different systems and measurements. This is particularly useful in scientific research and engineering, where energy calculations and conversions are essential in understanding and designing various systems and processes.

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