Isothermal, Adiabatic, Isobaric and Isochoric Processes
Four standard processes: constant temperature, no heat exchange, constant pressure and constant volume, each with its own work expression.
What is Isothermal, Adiabatic, Isobaric and Isochoric Processes?
Four standard processes: constant temperature, no heat exchange, constant pressure and constant volume, each with its own work expression.
Key formula / rule: Isothermal: DU = 0, W = nRT ln(V2/V1).
Key points
- Compute work and heat for each standard process.
- Analyse P-V diagrams to determine net work in a cycle.
Common exam trap
Using PV = constant for an adiabatic process.
Definitions
- Term
Isothermal, Adiabatic, Isobaric and Isochoric Processes
- Meaning
Four standard processes: constant temperature, no heat exchange, constant pressure and constant volume, each with its own work expression.
- Term
Isothermal, Adiabatic, Isobaric and Isochoric Processes — explanation
- Meaning
Isothermal work is nRT ln(V2/V1) and adiabatic processes obey PV^γ = constant. On a P-V diagram the adiabat is steeper than the isotherm, and the area under the curve is the work done.
Learning objectives
Compute work and heat for each standard process.
Analyse P-V diagrams to determine net work in a cycle.
Formulae
- Key point
Isothermal: DU = 0, W = nRT ln(V2/V1).
- Key point
Adiabatic: Q = 0, PV^γ = constant, W = (P1V1 - P2V2)/(γ - 1).
- Key point
Isochoric: W = 0, so Q = DU.
Prerequisites
PHY-U3-THR-T2-S1-C1
Common mistakes
Using PV = constant for an adiabatic process.
Forgetting that work is zero in an isochoric process.
Keywords
Isothermal
Adiabatic
Isobaric
Isochoric
Processes
Practice preview
What is the work done by an ideal gas during an isochoric process?…
easy
One mole of an ideal gas expands isothermally and reversibly from a volume of 10 L to 20 L at 300 K. Calculate the work done by the gas. (Given: R = 8.314 J mol-1 K-1, ln(2) = 0.693)…
medium
Which of the following statements about thermodynamic processes is INCORRECT?…
hard