Thermodynamics: sign convention

  • #1
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Main Question or Discussion Point

In physics book, if work is done by the system, it is positive
in my chemistry book, if work is done by the system, it is taken as negetive.
when I asked my chemistry teacher, he said the sign convention is different in physics and chemistry.
but why are they different?
 

Answers and Replies

  • #4
DrDu
Science Advisor
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The convention of your physics book is not conventional for theoretical physics, however, it is often used in engineering thermodynamics.
In physics and chemistry, one considers the change of the internal energy of the system. So if work is done on the system, work is counted positive.
Same for heat, which is positive if heat is entering the system. On the other hand enigneers are usually interested in the work done by an engine when some heat is input.
Hence they use different sign for work and heat.
 
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