Physical Equilibria

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An introduction to saturated vapor pressure, Raoult's Law, and to several types of phase diagrams - including phase diagrams for pure substances, solutions of non-volatile solutes, eutectic mixtures, systems of two miscible liquids (including fractional distillation), and systems of two immiscible liquids (including steam distillation).

• Fractional Distillation of Ideal Mixtures
This page explains how the fractional distillation (both in the lab and industrially) of an ideal mixture of liquids relates to their phase diagram.
• Fractional Distillation of Non-ideal Mixtures (Azeotropes)
Remember that a large positive deviation from Raoult's Law produces a vapor pressure curve with a maximum value at some composition other than pure A or B. If a mixture has a high vapor pressure it means that it will have a low boiling point. The molecules are escaping easily and you won't have to heat the mixture much to overcome the intermolecular attractions completely.
• Immiscible Liquids and Steam Distillation
This page looks at systems containing two immiscible liquids. Immiscible liquids are those which won't mix to give a single phase. Oil and water are examples of immiscible liquids - one floats on top of the other. It explains the background to steam distillation and looks at a simple way of carrying this out.
• Liquid-Solid Phase Diagrams: Salt Solutions
This page looks at the phase diagram for mixtures of salt and water - how the diagram is built up, and how to interpret it. It includes a brief discussion of solubility curves.
• Liquid-Solid Phase Diagrams: Tin and Lead
This page explains the relationship between the cooling curves for liquid mixtures of tin and lead, and the resulting phase diagram. It also offers a simple introduction to the idea of a eutectic mixture.
• Non-Ideal Mixtures of Liquids
This page looks at the phase diagrams for non-ideal mixtures of liquids, and introduces the idea of an azeotropic mixture (also known as an azeotrope or constant boiling mixture). It goes on to explain how this complicates the process of fractionally distilling such a mixture.
• Phase Diagrams for Pure Substances
This page explains how to interpret the phase diagrams for simple pure substances - including a look at the special cases of the phase diagrams of water and carbon dioxide.
• Raoult's Law and Ideal Mixtures of Liquids
This page deals with Raoult's Law and how it applies to mixtures of two volatile liquids. It covers cases where the two liquids are entirely miscible in all proportions to give a single liquid - NOT those where one liquid floats on top of the other (immiscible liquids). The page explains what is meant by an ideal mixture and looks at how the phase diagram for such a mixture is built up and used.

This page titled Physical Equilibria is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Jim Clark.