Thermodynamic Processes

Quasi-static thermodynamic evolutions: isothermal, isobaric, isochoric, and adiabatic processes.

General idea of the topic

Each thermodynamic process fixes one variable constant and lets the others evolve according to the first law. This topic classifies the four basic ideal-gas processes and how to calculate heat, work, and internal energy change in each one.

What you will truly understand

• Why in an isobaric process the work is simply P·ΔV, since pressure remains constant.
• Why in an isochoric process there is no work, and all the heat becomes internal energy change.
• Why in an isothermal process the ideal gas's internal energy does not change, and all the heat becomes work.
• Why in an adiabatic process there is no heat exchange, and the work is paid for entirely by internal energy.

Recommended learning route

1. Isobaric: constant pressure.
2. Isochoric: constant volume.
3. Isothermal: constant temperature.
4. Adiabatic: no heat exchange.

Physical criterion you must acquire

First identify which of the four variables (P, V, T, Q) stays constant or zero in the process: that choice automatically determines which terms of the first law vanish and simplifies the calculation.

Connection with real problems

Heat engine cycles (Otto, Diesel, Carnot) are built by chaining exactly these four basic processes, each modeling a real phase of compression, combustion, or expansion.

Final goal of the topic

Recognize each process by its constant variable, calculate heat and work in any of the four, and use them as building blocks to analyze complete thermodynamic cycles.