Isobaric Process
Definition
A thermodynamic change at constant pressure — like heating gas in a cylinder with a freely moving piston.
Unit: J (work)
Technical definition
A process with ΔP = 0. Work done is simply W = PΔV, and heat added goes partly into work and partly into internal energy (first law: Q = ΔU + W). Charles's law (V/T = constant) describes ideal gases under isobaric conditions.
Example
Boiling water in an open pot: pressure stays at 1 atm while the steam expands against the atmosphere, doing PΔV work as it forms.
Common confusion
Constant pressure does not mean no work — expanding gases at constant pressure do plenty of work (W = PΔV). ‘Isobaric’ constrains pressure, not volume or temperature.