National Council of Examiners for Engineering and Surveying (NCEES) Fundamentals of Engineering (FE) Chemical Practice Exam

Relative volatility is defined as the ratio of the mole fractions of two components in one phase to those in another phase, specifically in a mixture undergoing phase separation, such as in distillation processes. This measure provides insight into how easily one component can be separated from another based on their differing volatilities.

When a liquid mixture is heated, the more volatile component preferentially vaporizes, and relative volatility quantifies this preference. A higher relative volatility suggests that one component can be separated more readily from the other, making it a crucial concept in chemical engineering, particularly in designing and optimizing separation processes like distillation columns.

The other options do not correctly capture the essence of relative volatility. The first option refers to pressure and temperature, which are related to phase behavior but do not define volatility. The third option about mass to volume does not relate to the separation characteristics of components in a mixture. The last option discusses temperature change over fixed pressure, which is pertinent to thermodynamic processes, but not to the specific concept of relative volatility in separation processes.