What is the highest temperature at which vapor can be liquefied regardless of the applied pressure called?

The highest temperature at which vapor can be liquefied regardless of the applied pressure is defined as the critical temperature. At this temperature, the distinctions between liquid and gas phases disappear, and the substance can no longer exist as a liquid, no matter how much pressure is applied.

Understanding critical temperature is crucial, especially in refrigeration and thermodynamics, because it indicates the maximum temperature at which a substance can transition into a liquid form. This concept is essential for designing and operating systems that utilize refrigerants, as it directly impacts the efficiency and operational limits of refrigeration cycles.

The boiling point refers to the temperature at which a liquid becomes a gas at a specific pressure, but it does not account for varying pressures in the way critical temperature does. Similarly, the melting point pertains to the transition from solid to liquid, while the evaporation point describes the phase change from liquid to vapor at specific conditions. Therefore, these terms don't capture the same essential characteristics as critical temperature does.