why sign conventions for work done on the system and by the system is different in physics and chemistry?

Asked by  | 7th Dec, 2012, 10:53: PM

Expert Answer:

It's sometimes easier to find the change in energy first (whether +ve or -ve) and decide whether it is positive or negative afterwards.

energy lost ===> ?E is negative ==> work done by system
energy gained => ?E is positive ==> work done on system 

A good example is the first law of thermodynamics:

change in internal energy = heat added to system - work done by system; OR, equivalently:
change in internal energy = heat added to system + work done on system

Answered by  | 8th Dec, 2012, 08:45: AM

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