In my chemistry book I always see a dot for units. For example, atm•L. Does this mean “1 atm per Liter?” By Atm I mean atmospheric pressure, not atom.


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  • $\begingroup$ dah... Thanks for the correction! // Yes $\mathrm{atmospheres}\space\times\space\mathrm{liter}$ $\endgroup$ – MaxW Jul 29 '18 at 21:52
  • $\begingroup$ @MaxW How do you conceptualize that? Im just confused on that. Does this mean the unit of pressure in regard to one liter ? If you know what im saying? $\endgroup$ – user64524 Jul 29 '18 at 21:54
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    $\begingroup$ 101.33 Joules = 1 l atm // You have to bust "complex" units down to primitives. So a liter is 1000 cm^3 and so on. Then rearrange to something that makes more sense. The whole think is called dimensional analysis. $\endgroup$ – MaxW Jul 29 '18 at 22:01
  • $\begingroup$ @MaxW okay. I know dimensional analysis but when there are two units it’s confusing. So really atm•L needs to be broken down to make sense, more or less? Is that kind of what you mean. $\endgroup$ – user64524 Jul 29 '18 at 22:24
  • $\begingroup$ atm-l presumably showed up in some formula. You wouldn't want to willy-nilly convert atm-l to joules without doing a dimensional analysis on the rest of the formula. The formula itself may be trying to solve for temperature. $\endgroup$ – MaxW Jul 29 '18 at 22:30

$\mathrm{atm \cdot L}$ is a derived unit for energy. Pressure is defined as being force/area, and volume is distance cubed. If you multiply out the units of these quantities, you can see it is equivalent to force times distance, i.e. work, measured in energy.

  • $\begingroup$ Is there a particular context where atm⋅L (or pressure⋅volume more generally) is the "natural" way to express a quantity of energy? $\endgroup$ – R.M. Jul 30 '18 at 18:45
  • $\begingroup$ @R.M. see the new link $\endgroup$ – ringo Jul 30 '18 at 18:58
  • $\begingroup$ @ringo What do you mean by “If you multiply out these units?” $\endgroup$ – user64524 Aug 4 '18 at 19:10
  • $\begingroup$ I am talking about performing dimensional analysis. Consider measuring the area of a sheet of paper. You multiply its length by its width (both measured as distances) and you get its area in terms of distance squared. Read more about it here: physicsabout.com/dimensional-analysis-physics $\endgroup$ – ringo Aug 4 '18 at 19:16

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