Thermodynamics: sign convention

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SUMMARY

The discussion highlights the differing sign conventions for work in thermodynamics as presented in physics and chemistry. In physics, work done by the system is considered positive, while in chemistry, it is viewed as negative. This discrepancy arises because physics focuses on internal energy changes, whereas engineering thermodynamics emphasizes work output from engines. Adhering to a consistent convention is crucial for clarity in calculations and interpretations.

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  • Understanding of the First Law of Thermodynamics
  • Familiarity with internal energy concepts
  • Knowledge of engineering thermodynamics principles
  • Basic principles of heat transfer
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  • Research the First Law of Thermodynamics in detail
  • Learn about the differences between physics and chemistry conventions in thermodynamics
  • Explore engineering thermodynamics applications and their sign conventions
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AdityaDev
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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?
 
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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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