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Isobaric Process

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Definition: An isobaric process is a thermodynamic process in which the pressure remains constant. This is usually obtained by allowed the volume to expand or contract in such a way to neutralize any pressure changes that would be caused by heat transfer.

In an isobaric process, there are typically internal energy changes, work is done by the system, and heat is transferred, so none of the quantities in the first law of thermodynamics readily reduce to zero. However, the work at a constant pressure can be fairly easily calculated with the equation:

W = p * delta-V
Since W is the work, p is the pressure (always positive) and delta-V is the change in volume, we can see that there are two possible outcomes to an isobaric process:
  • If the system expands (delta-V is positive), then the system does positive work (and vice versa)
  • If the system contracts (delta-V is negative), then the system does negative work (and vice versa)

Isobaric Process & Phase Diagrams

In a phase diagram, an isobaric process would show up as a horizontal line, since it takes place along a constant pressure.
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