Process-path constraints vocabulary: An isobaric process is one carried out at constant __________.

Introduction:
Thermodynamic analyses often classify processes by which property is held constant: isothermal (T), isobaric (P), isochoric (V), isentropic (S), or isenthalpic (H). Correctly identifying these terms is foundational for applying the first and second laws to real equipment like compressors, turbines, valves, and heat exchangers.

Given Data / Assumptions:

• Steady or unsteady processes may be idealized with one property held constant.
• No specific working fluid is required to define the term.

Concept / Approach:
“Isobaric” literally means “equal pressure.” In an isobaric process, the system pressure remains constant throughout, while other properties such as temperature, volume, enthalpy, and entropy may change according to the path and heat/work interactions. Examples include boiling/condensing at constant pressure and many mixing operations open to atmosphere.

Step-by-Step Solution:
Match the prefix: iso (same) + baric (pressure).Conclude the held property is pressure.Select “pressure” as the correct completion.

Verification / Alternative check:
Property diagrams (P–V, T–S) show horizontal lines for isobaric paths on P–V coordinates.

Why Other Options Are Wrong:

• Temperature → isothermal; volume → isochoric/isochoric; entropy → isentropic; enthalpy → isenthalpic (e.g., throttling).

Common Pitfalls:
Confusing isentropic (adiabatic and reversible) with isothermal; they are distinct idealizations.

Final Answer:
pressure