in ncert chem. it is given that work done on the system is +ve and by the system  -ve

BUT

in ncert physics work done on the system -ve and by the system +ve

 

which one is true?

what happens actually is that when we study chemistry then we study the effects of any change "ON THE SYSTEM" and hence when work is done on the system we suppose that energy is gained by the system and hence it is taken as +ve and when energy is lost i.e. work is one by the system then it is taken as -ve . Whereas in physics we observe the effect of change on the surroundings , hence when work is done by the system, energy is gained by surroundings and hence is taken as +ve in physics and whn work is done on the sys. it is taken as -ve coz surroundings lose energy. i hope the sign convension is clear now

(pls do rate me if u accept the answer)

it is true

it is the convention as    in chemistry we take in concideration the extarnal work performed on the system and take it as +ve...........

but in phy. we talk about the internal work and take the work performed by the system as +ve

Let's make things a little bit clear !!

 

Work done by what ?

 

If  we consider a gas is expanding against a force ( say the wt of a piston )

 

Then work done BY the gas is +ve , BY the wt is -ve .

 

Work done  ON the gas ( BY the wt ) is clearly -ve & Work done on the mass ( BY the gas ) is +ve .

 

There is no arbitrariness ( no sign convension , dW = always F . ds )

 

Hope it is clear now !

 

So from the context try to grasp whose work  done is concerned .