24: Solutions I - Volatile Solutes
- Page ID
- 11820
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- 24.1: A Mixture is a Combination of Two or More Substances
- Since mixtures are comprised of two or more substances, we often use partial molar quantities, such as the partial molar volume, molality, or mole fractions, to describe their behavior and properties (e.g. composition, \(T\), and \(P\)). Mixtures can consist of multiple gases, multiple liquids, multiple solids, or even liquids and gases mixed together.
- 24.2: The Gibbs-Duhem Equation Relates Chemical Potential and Composition at Equilibrium
- The Gibbs-Duhem equation relates how the chemical potential can change for a given composition while the system maintains equilibrium. So for a binary system, consisting of components A and B (the two most often studied compounds in all of chemistry)
- 24.3: Chemical Potential of Each Component Has the Same Value in Each Phase in Which the Component Appears
- Chemical potential tells how energy, such as the Gibbs function, changes as the composition of the mixture changes. As systems seek to minimize Gibbs energy, we can use the chemical potential of a mixture to determine the direction of equilibrium.
- 24.4: Ideal Solutions obey Raoult's Law
- Liquids tend to be volatile, and as such will enter the vapor phase when the temperature is increased to a high enough value, provided they do not decompose first. A volatile liquid is one that has an appreciable vapor pressure at the specified temperature. The composition of an ideal mixture containing at least one volatile liquid can be described using Raoult’s Law.
- 24.5: Most Solutions are Not Ideal
- The Gibbs-Duhem equation relates how the chemical potential can change for a given composition while the system maintains equilibrium. So for a binary system, consisting of components A and B (the two most often studied compounds in all of chemistry)
- 24.6: Vapor Pressures of Volatile Binary Solutions
- The behaviors of ideal solutions of volatile compounds follow Raoult’s Law. Henry’s Law can be used to describe the deviations from ideality.
- 24.7: Activities of Nonideal Solutions
- As seen before activities are a way to account for deviation from ideal behavior while still keeping the formulism for the ideal case intact.
- 24.8: Activities are Calculated with Respect to Standard States
- The thermodynamic activity, \(a\) , is the effective concentration of a species in a mixture. It is a dimensionless quantity that are calculated with respect to standard states.
- 24.9: Gibbs Energy of Mixing of Binary Solutions in Terms of the Activity Coefficient
- At low temperatures, there will be a solubility limit of substance 1 into substance 2 and vice versa. At higher temperatures the two components can mix completely as entropy becomes more important. At the transition between these two regimes we will have critical or consolute point.