Behavior of superheated vapor: A superheated vapor most closely behaves like which idealized substance?

Introduction / Context:
When a vapor is heated significantly above its saturation temperature at a given pressure, it is called superheated. Engineers often approximate superheated vapors as ideal (perfect) gases to simplify property evaluations and process calculations.

Given Data / Assumptions:

• Vapor well above saturation line at the working pressure.
• Moderate pressures where intermolecular forces are relatively weak.
• Use of standard correlations or tables when necessary.

Concept / Approach:
Far from the saturation dome, compressibility factors approach unity and the ideal-gas equation pV = mRT becomes an adequate approximation. Thus, a superheated vapor behaves similarly to a perfect gas, allowing the use of cp, cv, and R with minimal error for many engineering calculations (though property tables remain more accurate near saturation or at very high pressures).

Step-by-Step Solution:

Verification / Alternative check:
Comparison of superheated-steam table values with ideal-gas estimates at moderate pressure shows small deviations, validating the approximation away from the dome.

Why Other Options Are Wrong:

• Air/steam/ordinary gas: These labels are either specific substances or vague terms; the intended idealized behavior is the perfect gas model.

Common Pitfalls:
Using ideal-gas relations too close to saturation or at very high pressures, where real-gas effects become significant.

Final Answer:
perfect gas