Free Expansion — Sudden Expansion into a Vacuum Evaluate the statement: “When a fluid is allowed to expand suddenly into a vacuum chamber through a large orifice, the process is called free expansion.”

Introduction / Context:
Free expansion (also called Joule free expansion in gases) is a classic irreversible process used to illustrate energy and entropy changes when a fluid expands without doing external work and without heat transfer. Recognizing this process helps differentiate it from throttling and isentropic expansion.

Given Data / Assumptions:

• The fluid initially occupies part of a vessel; a partition or valve is opened to a vacuum chamber.
• No external resistance is overcome (no work done on surroundings).
• Process is rapid and adiabatic; heat transfer during the brief event is negligible.

Concept / Approach:
In free expansion into vacuum, external pressure is essentially zero. Thus boundary work W = ∫ p_ext dV ≈ 0. In an insulated setup, Q = 0. For an ideal gas, internal energy depends only on temperature; since ΔU = Q - W = 0, the temperature of an ideal gas remains unchanged. However, entropy increases because the process is highly irreversible due to unrestrained expansion and mixing of states.

Step-by-Step Solution:
Identify key features: unresisted expansion into vacuum; large opening implies negligible throttling effects.Apply first law: ΔU = Q - W; with Q = 0, W = 0 ⇒ ΔU = 0 for ideal gas.Conclude the process name: “free expansion.”

Verification / Alternative check:
Contrast with throttling: throttling involves flow through a restriction with p_drop and h ≈ constant; free expansion is a non-flow, unresisted expansion, not a steady-flow throttling process.

Why Other Options Are Wrong:
Calling the statement false would deny the standard thermodynamic terminology for this well-known experiment.

Common Pitfalls:
Equating free expansion with nozzle or turbine expansion; assuming temperature must always drop—only true for real gases under certain conditions, not for ideal gases.

Final Answer:
True