Which of the following describes how latent heat of vaporization is measured?

The measurement of latent heat of vaporization is primarily concerned with the quantity of heat required to convert a unit mass of a substance from liquid to vapor without changing its temperature. This is typically quantified in terms of energy per mass, such as BTUs or calories per pound (or kilogram).

When considering the options, the focus on the amount of water in pounds indicates that the measurement is based on the mass of the substance undergoing the phase change. By measuring the quantity of water and applying the latent heat value for water, one can determine the total energy absorbed in the process of vaporization.

Hence, the correct answer reflects the fundamental principle that the latent heat of vaporization is directly related to the mass of the water being vaporized, illustrating a core concept in thermodynamics related to phase changes. This understanding is crucial for applications in commercial food equipment, where precise calculations of energy consumption and efficiencies are essential.