Thermodynamics: sign convention

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Discussion Overview

The discussion centers around the differing sign conventions for work in thermodynamics as presented in physics and chemistry contexts. Participants explore the implications of these conventions on the understanding of thermodynamic processes, particularly in relation to the first law of thermodynamics.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant notes that in their physics book, work done by the system is considered positive, while in their chemistry book, it is regarded as negative.
  • Another participant suggests that the difference in sign conventions is acknowledged by a chemistry teacher, who states that physics and chemistry have different conventions.
  • Some participants propose that any convention can be used as long as it is applied consistently.
  • One participant argues that the physics convention is not standard for theoretical physics but is commonly used in engineering thermodynamics, where work done on the system is counted as positive.
  • It is mentioned that in physics and chemistry, work and heat are considered positive when they enter the system, contrasting with engineering perspectives that focus on work done by an engine.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness and application of sign conventions in physics versus chemistry, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

The discussion highlights the potential confusion arising from different definitions and applications of sign conventions in various fields, which may depend on the context of the study (theoretical vs. applied). Unresolved assumptions regarding the implications of these conventions are present.

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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