Solution thermodynamics — Raoult’s law applies directly to which component in a liquid solution?

Introduction:
Vapor–liquid equilibrium calculations often combine Raoult’s law and Henry’s law. Knowing when each applies avoids serious errors in estimating partial pressures. This question asks which component obeys Raoult’s law in the typical dilute-solution framework.

Given Data / Assumptions:

• Binary or multicomponent liquid solution with a volatile solvent and dilute solute.
• Near-ideal behavior for the solvent (activity coefficient ≈ 1).
• Temperature below critical and within VLE region.

Concept / Approach:

Raoult’s law states p_i = x_i * P_i^sat for components that behave ideally in the liquid phase—most notably the solvent at moderate dilution. The dilute solute, especially when it deviates from ideality, is better described by Henry’s law p_i = x_i * H_i. Non-volatile solutes have negligible vapor pressure and do not follow Raoult’s law in any useful sense.

Step-by-Step Solution:

Verification / Alternative check:

Textbook VLE examples (ethanol–water near ideality) apply Raoult’s law to both at moderate composition; in dilute solutions, the solvent specifically fits Raoult, while solute tends to Henry behavior.

Why Other Options Are Wrong:

A is overbroad; B is contradictory; C describes a component with negligible vapor pressure; E generally uses Henry’s law constants for gases dissolved in liquids.

Common Pitfalls:

Applying Raoult’s law to dilute, highly non-ideal solutes; neglecting activity coefficients when deviations from ideality are significant.

Final Answer:

solvents