In an equilibrium state, which variable would be used to represent the liquid composition?

In the context of phase equilibrium in a chemical process, the variable that typically represents the liquid composition is denoted as X, specifically in the format X1* or X2*. This notation indicates the molar fraction of a component in the liquid phase at equilibrium conditions.

Choosing X1* suggests that it refers to the composition of the first component in the liquid phase at equilibrium. This is consistent with the convention in thermodynamics and chemical engineering where liquid compositions are symbolized using X, while gas compositions are represented by Y.

At equilibrium, the liquid and vapor phases have specific compositions that correspond to the same temperature and pressure conditions. The asterisk (*) indicates that this is the composition at equilibrium, which is crucial in phase diagrams and calculations related to phase behavior, such as in distillation or absorption processes.

Understanding this distinction is important for analysis and process design, where knowing the liquid composition at equilibrium informs decisions about separation processes and material balances.