At what pressure are melting points typically determined?

Melting points are typically determined at atmospheric pressure, which is the standard pressure at sea level (approximately 101.3 kPa or 760 mmHg). This standardization allows for consistent and reproducible results when measuring the temperature at which a solid transitions to a liquid.

Atmospheric pressure provides a stable environment for the phase transition to occur without external influences, making the measurement reliable. Under significantly altered pressure conditions, such as high or vacuum conditions, the melting point can be affected, causing discrepancies in the data. This is particularly important in laboratory settings where precise measurements are necessary for the reproducibility of experiments and for the identification of substances based on their melting points. Thus, the correct answer aligns with the standard practices in both research and education concerning the determination of melting points.