Definition of Heat and the First Law of Thermodynamics (discrepancy?)

[JC2000]

Zemansky defines Heat as : When a closed system whose surroundings are at a different temperature and on which diathermic work may be done undergoes a process, then the energy transferred by non mechanical means, equal to the difference between the change in internal energy and the diathermic work is called heat. $Q= \Delta U - W$(diathermic).

But the First Law of Thermodynamics states : $Q = \Delta U + W$

Is the discrepancy because for diathermic work, $W = -W$?

 

[DrClaude]

It depends on the convention used. Is $W$ the work performed by the system or on the system?

 

[JC2000]

It depends on the convention used. Is $W$ the work performed by the system or on the system?

Oh! I see now! Thanks!

Regarding conventions :

For Physics :
If Heat is absorbed/added to the system = Work on the system by the surroundings = System expands=$=+ W$
If Heat is released by the system = Work by the system on the surroundings = system contracts $=-W$

For Chemistry : The reverse applies

Is my understanding correct?
Is the reversal for Chemistry simply by convention, or is there some specific purpose?

 

[Chestermiller]

It depends on the book. In Denbigh, an obvious chemistry text, he uses what you refer to as the Physics convention

 

[JC2000]

It depends on the book. In Denbigh, an obvious chemistry text, he uses what you refer to as the Physics convention

So there isn't an official set of guidelines from IUPAC or a clear consensus in the Physics and Chemistry communities?
Also, just to be clear, I am correct regarding the sign convention for work done by system/on the system with reference to Physics?

 

[Chestermiller]

In your "physics convention," W is the work done by the surroundings on the system. In the other convention, W is the work done by the system on the surroundings. These definitions are independent of whether expansion or compression is occurring.