Dear Piyush
In thermodynamics we have two things :- System and Surrounding
Work(System) + Work(surrounding) = Zero
so, Work(System) = - Work(Surrounding)
Similarly, Heat evolved/absorbed(System) = - Heat evolved/absorbed(Surrounding)
So if you consider one thing (say System) to be of positive sign convention then other thing (Surrounding) becomes negative in sign convention
In physics we give more importance to System. For example we calculate forces, acceleration, velocity etc of a body which constitutes System. Hence System becomes reference in physics. So we give positive sign convention for System.
In Chemistry we give more importance to Surroundings. For example we calculate temperature, pressure etc. of the gases which constitutes Surroundings. Hence Surroundings becomes reference in Chemistry. So we give positive sign convention for Surroundings.
Regards
Arun (askIITians forum expert)
