Thermodynamics Lecture Notes

PV Diagrams

• P stands for pressure, V stands for volume.
• Diagram represents the relationship between pressure and volume at any given instant.
• Example: Container with gas and a movable piston.
  • Piston movement affects volume and pressure.

Piston Movement

• Piston Down: Decreases volume, potential increase in pressure.
• Piston Up: Increases volume, potential decrease in pressure.
• Graph movement:
  • Piston down → left on the graph.
  • Piston up → right on the graph.

Thermodynamic Processes

• Multiple paths possible on a PV diagram.
• Infinitely many ways for gas to change state.

Four Common Thermodynamic Processes

1. Isobaric Process
   • Iso = constant, Baric = pressure.
   • Constant pressure process.
   • Represented by horizontal line on PV diagram.
   • Types:
     • Isobaric Expansion: Volume increases, moves right.
     • Isobaric Compression: Volume decreases, moves left.

Area Under the Curve

• Work Representation

  • Area under curve represents significant physical quantities.
  • For isobaric, area = pressure × change in volume (PΔV).

• Physical Explanation

  • Pressure (P) is force per area.
  • Volume change represented by height × area of piston.
  • Work = force × distance (height change).
  • Area under isobaric process represents work done by/on gas.
  • Positive area implies work done by the gas.
  • Negative area implies work done on the gas.

Calculating Work

• Formula: Work done by gas = PΔV.
• First Law of Thermodynamics: ΔU = Q + W.
  • W is work done on the gas.
  • For isobaric, W = -PΔV (work done on gas).

Practical Setup for Isobaric Process

• Heat is added; piston moves to maintain constant pressure.
• Pressure equilibrates with atmospheric pressure and piston weight.

Conclusion

• Detailed explanation of isobaric process.
• Preparation for next lecture on remaining thermodynamic processes.