isobaric

Isobaric is an adjective describing processes or phenomena that occur at constant pressure. It is used in physics, chemistry, and meteorology to denote situations where pressure remains unchanged while other variables may change.

In thermodynamics, an isobaric process is one in which the pressure stays fixed while temperature, volume, and internal energy can vary. For an ideal gas, P = nRT/V implies that, at constant P, volume is proportional to temperature. When heat is added at constant pressure, the heat transfer equals the molar heat capacity at constant pressure times the temperature change (Q = n Cp ΔT), and the work done by the system is W = P ΔV. The enthalpy change is ΔH = n Cp ΔT for an ideal gas, linking heat input directly to temperature rise.

In meteorology, isobars are lines on weather maps that connect points of equal atmospheric pressure, allowing meteorologists to visualize pressure systems. The spacing of isobars indicates the pressure gradient; closely spaced lines signal strong winds, while widely spaced lines indicate lighter winds. Isobaric surfaces are conceptual zones of constant pressure within the atmosphere or within modeling frameworks.

In experimental chemistry and physics, isobaric conditions are achieved using constant-pressure calorimetry, where reactions are studied at a fixed external pressure. This is in contrast to constant-volume methods, such as bomb calorimetry, where the volume is kept fixed and pressure can vary.

Etymology derives from the Greek iso, equal, and baros, weight or pressure.