Work Done by Gas: Pexternal*dV?

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SUMMARY

The work done by gas during expansion against a constant external pressure is calculated using the formula W = Pexternal*dV. However, the internal pressure of the gas (Pgas) must also be considered, as the work done is derived from the force exerted by the gas on the piston. The correct approach involves integrating the internal pressure over the volume change, expressed as W = ∫ P dV from v1 to v2. This distinction clarifies the mechanics of gas expansion in a container.

PREREQUISITES
  • Understanding of thermodynamic principles
  • Familiarity with the concept of pressure in gases
  • Knowledge of calculus for integration
  • Basic mechanics of pistons and forces
NEXT STEPS
  • Study the principles of thermodynamics, focusing on the first law
  • Learn about the relationship between pressure and volume in gases
  • Explore integration techniques in calculus, particularly in physical applications
  • Investigate the mechanics of pistons and their role in gas expansion
USEFUL FOR

Students of physics, engineers working with thermodynamic systems, and anyone interested in understanding gas behavior during expansion processes.

suli
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if gas in a container expands against a constant external pressure,
the work done by it is Pexternal*dV.
but the force is generated inside the container, shouldn't we use Pgas to calculate the answer?
 
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You are mistaken (unless you have stated the problem incorrectly). The work done by the expanding gas would be

[tex]W = \int p dV[/tex] over the range from v1 to v2 and p would be the internal pressure.
 
The piston is exerted upon by two pressures, one from the atmosphere or other gas (if any) and the second from the gas inside the chamber. The work done by the gas on the piston comes from the definition of work done by a force. This should solve your problem. Work done by a gas would obviously involve then, the force exerted BY the gas on the piston.
 

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