Isothermal Process
A thermodynamic change in state occurring at a constant temperature throughout the system.
Governing formula
ΔT = 0 ⇒ ΔU = 0, Q = W = n R T ln(V2/V1)
SI unit
J
In depth
For an ideal gas undergoing isothermal expansion, internal energy remains constant (ΔU = 0), so all heat added Q is fully converted into expansion work W.
Examples in the real world
Slow expansion of gas in a thin-walled metal cylinder immersed in a massive constant-temperature water bath.