Isotermisk

Isotermisk is a term used in thermodynamics to describe a process or condition in which the temperature of a system remains constant. The word combines the Greek roots iso meaning equal and therm- meaning heat. In practice, an isotermisk process requires heat exchange with the surroundings to offset any changes in temperature that would otherwise occur.

In the ideal gas model, an isothermal process has the property that temperature T is constant, so the product of pressure and volume satisfies PV = nRT with T fixed. Because the internal energy of an ideal gas depends only on temperature, ΔU = 0 during an isothermal change. Consequently, all heat added to the gas becomes work done by the gas: Q = W = nRT ln(V2/V1). Such processes are typically slow and quasi-static to maintain equilibrium throughout the change.

Isotermiska processes are contrasted with isochoric (constant volume), isobaric (constant pressure), and adiabatic (no heat exchange) processes. In practice, maintaining a strictly isotermisk condition can be challenging due to heat transfer limitations, but it is a useful idealization for analyzing cycles such as the isothermal stages of the Carnot cycle.

Beyond thermodynamics, the term isotermisk appears in geology and meteorology in related forms such as isotherms, lines on maps that connect points of equal temperature. The concept similarly centers on the idea of constant temperature, applied across different scientific contexts.