Table of Contents
Thermodynamic Processes Overview
A thermodynamic process changes a system's state (P, V, T, U). The four fundamental ideal gas processes are: isothermal (constant T), isobaric (constant P), isochoric (constant V), and adiabatic (no heat exchange). These are building blocks of engine cycles like Carnot, Otto, Diesel, and Rankine.
The first law (Q = W + dU) governs each process. Understanding which quantities are zero or constant for each process simplifies analysis. On a PV diagram, work equals the area under the process curve.
Equations
Isothermal: W = PV ln(V2/V1), ΔU = 0
Isobaric: W = PΔV
Isochoric: W = 0
Adiabatic: PVγ = const, Q = 0
Comparison
| Process | Constant | W | Q |
|---|---|---|---|
| Isothermal | T | nRT ln(V2/V1) | =W |
| Isobaric | P | PΔV | nCpΔT |
| Isochoric | V | 0 | nCvΔT |
| Adiabatic | Q=0 | -ΔU | 0 |
FAQ
What is gamma?
γ = Cp/Cv. Monatomic: 5/3=1.667. Diatomic (air): 7/5=1.4. Polyatomic: ~1.3.