Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Physics/Chem: Why the sign difference in Thermodynamics?

  1. Feb 5, 2010 #1
    I have been wondering why we take work done on the system +ve in chemistry while -ve in physics. Similar difference exist for many other quantities. Can you explain why the difference exists?
     
  2. jcsd
  3. Feb 6, 2010 #2
    There is no difference unless the Chemists are erring.

    Physics always works from the system's point of view. The system is normally your gas or solution or what have you. Work done by the system pushing pistons, swirling wheels counts negative, because the system loses energy. And you can drive stuff with it. When you push the piston or turn the wheel from the outside then you put energy into the system so it counts positive.
    Same for heat, heating the system positive cooling the system negative.

    The reasons why things may disagree can be:
    - You are talking about different systems
    - Canonical transforms. If you use a different potential then the formulas look very similar, but are in fact different.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook