30Yeah.. the convention is just opposite in Physics and Chemistry.
plz read follwoing with reference to jee books :
IUPAC RULES:
In thermodynamics as per IUPAC:(i)Work done by system=negative and (ii)first law is ∂U=∂Q+∂W
CLASSIC TEXTS[HC VERMA]:
(i)Work done by system=positive and (ii)first law is ∂U=∂Q-∂W.
Now with respect to JEE PHYSICS THERMODYNAMICS AND JEE CHEMISTRY THERMODYNAMICS QUESTIONS WHAT CONVENTION WE MUST FOLLOW?
to be precise,if we are asked work done in some process by system do we have to use convention as per IUPAC or not??
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11 Answers
1Chem & Physics follow opposite conventions for work done.
In Chemistry, the equations are with respect to the gas (the system ??). So, the work done on it increases its energy and hence, is positive +ve.
Work done by it decreases its energy and is -ve.
In Physics, we take stuff with respect to the surroundings.
Work done on the gas/system reduces the energy of the surroundings and is -ve.
Work done by the gas/system increases the energy of the surroundings and is +ve.
PS: er... I think you must know.... I'm no expert. :P
Nonetheless, most probably, I am correct. (I hope. '~')
1@atomsurfer so u mean to say that if we consider work done by gas in chemistry it is negative and in physics it is positive [3][3][3]
30
49i think this is a thread that is posted by at least one asirant of each batch every year! :P
If i am not wrong this was asked by Ashish himself once!! (:P)
In JEE no one is going to ask you how u did a sum...or etc etc and boards do not have this chapter..so chill! :P
You are free to use any ONE convention of your choice but make sure you follow that THROUGHOUT and do not mess up between the two.!
As of me i use the physics one because i had studied thermodynamics in physics first! :P :P
1@ SUbho- You have to follow different conventions for different subjects. If you don't you will lose marks in those bloody signs.
1@swordfish
exactly thts why i underlined word WORK...because it is there for work that the sign matter[1]
as of internal energy we get same using both approaches
49:P
yeah so i did in class-11
but i am not losing marks whatever convention i use in FIITJEE AITS!
i know both but who cares??
both give same answers!!
1@asish
can u elaborate on sign used for work done in physics and chemistry clearly[1]...thanks!
30I guess what atomsurfer has said is correct. Otherwise, do what Subho says. I think he is right. Follow any one and keep it simple. :)
62absolutely as atomsurfer said...
just use that convention.. .
it is like using the right side as the positive infinity.. people may use the left side too but then it is a convention ;)