Physics/Chem: Why the sign difference in Thermodynamics?

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SUMMARY

The discussion addresses the contrasting conventions of work sign in thermodynamics between chemistry and physics. In physics, work done by the system is considered negative as it signifies energy loss, while work done on the system is positive, indicating energy input. Conversely, in chemistry, work done on the system is treated as positive, leading to potential confusion. This discrepancy arises from differing perspectives on the system and the application of canonical transformations, which can alter the interpretation of thermodynamic quantities.

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  • Understanding of thermodynamic systems and processes
  • Familiarity with the concepts of work and energy in physics
  • Knowledge of canonical transformations in thermodynamics
  • Basic principles of heat transfer in chemistry and physics
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ishan001
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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?
 
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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.
 

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