Isobaric System (work done by, or on?)

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    Isobaric System
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SUMMARY

The discussion centers on the concept of work in an isobaric system, specifically analyzing a graph of pressure versus volume (PxV) where pressure remains constant. The key equation referenced is U=Q-W, which relates internal energy (U), heat (Q), and work (W). It is established that if work (W) is greater than zero, the system is doing work on its surroundings, while if W is less than zero, work is being done on the system. This clarification addresses a common misconception regarding the relationship between heat and work in thermodynamic processes.

PREREQUISITES
  • Understanding of thermodynamic principles, particularly the first law of thermodynamics.
  • Familiarity with isobaric processes and their graphical representation.
  • Knowledge of the relationship between internal energy, heat, and work.
  • Basic proficiency in interpreting pressure-volume (PxV) graphs.
NEXT STEPS
  • Study the implications of the first law of thermodynamics in various thermodynamic processes.
  • Learn about isothermal and adiabatic processes for comparative analysis.
  • Explore the concept of work done in different thermodynamic systems, including closed and open systems.
  • Investigate the role of heat transfer in thermodynamic cycles, such as the Carnot cycle.
USEFUL FOR

Students of thermodynamics, physics educators, and anyone seeking to deepen their understanding of work and energy transfer in isobaric systems.

audilover
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Homework Statement



There is a graph PxV. Pressure is obviously constant so it is a strait line and volume is from point A (1) to point B (3.5). You do not need to solve anything but it asks if work is being done on the system or by the system.

Homework Equations



U=Q-W

The Attempt at a Solution



I thought work is being done on the system because when going from point A to point B you are increasing meaning your Q>0.
 
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Going from point A to point B, you are increasing what? Also, Q has nothing to do with whether work is being done on or by the system. Even if you solve this problem based on what I wrote below, it might be worth explaining what you were thinking originally. I'm guessing you have a common misconception that may be worth clearing up.

All you need to do for this problem is figure out the sign of W. If W>0, the work is subtracting from the internal energy U of the system, so work is being done by the system on its surroundings. Similarly, if W<0, work is done on the system.
 

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