Which is not a thermodynamic property of refrigerants?

• A. Boiling point
• B. Vapor pressure
• C. Flammability
• D. Critical temperature

Answer: (C)

The main idea is distinguishing properties that describe energy and phase behavior from those that describe safety and chemical reactivity. Boiling point, vapor pressure, and critical temperature are all thermodynamic properties because they tell you how a refrigerant behaves with heat and pressure—when it turns from liquid to vapor, the pressure a vapor exerts at a given temperature, and the temperature limit where liquid and gas phases can exist together. Flammability, however, relates to whether the substance can ignite and burn, which is a chemical safety property rather than a thermodynamic state property. So flammability is not a thermodynamic property, even though a refrigerant might be flammable or nonflammable.