Concepts.doc (Word 97)
KEY CONCEPTS FOR EXAM #2
Note: This list is only a guide to help you study. It is NOT comprehensive, and the exam may cover any topics discussed in class.
Classifications of Phase Transitions
 First Order Phase Transitions … the first derivatives of the chemical potentials are discontinuous at the transition
 Second Order … the first derivatives of the chemical potentials are continuous, but the second derivatives are discontinuous
 plots of relevant variables at the phase transition (e.g. C_{p} vs. Temp, etc)
Criteria for an Ideal Solution
 all intermolecular interactions are identical
 there is no change in volume upon mixing
 there is random mixing of components
Thermodynamics of Mixing
For ideal gases
Raoult's Law
or
or
where x_{i} is mole fraction of i in solution, g_{i} _{ }is the activity coefficient of i, P_{i} is the partial vapor pressure of i, and P_{i}* is the pressure of pure i.
 In an ideal solution, all intermolecular interactions (i.e. solutesolvent, solutesolute, solventsolvent) are identical
 Positive deviations from Raoult's Law occur when the interactions between the solute and the solvent are weaker than solutesolute and solventsolvent interactions. Typically, the solute molecules break up strong interactions of the solvent with itself.
 Negative deviations from Raoult's Law occur when the interactions between the solute and the solvent are stronger than solutesolute and solventsolvent interactions. The solvent and solute molecules decrease each other's escaping tendency.
Henry's Law (obeyed by solute in dilute solutions)
where k_{i} is Henry's Law constant, x_{i} is mole fraction of i in solution
 Henry's Law approximation is most accurate for dilute solutions (i.e. when the substance is a solute in low concentrations). Raoult's Law is most accurate for concentrated solutions (i.e. when the substance is a solvent in high concentration)
Composition of the Vapor
where Y_{i} is the mole fraction of component i in the vapor phase, and P_{total} is the total pressure of the vapor phase above the solution
Variations of Equilibrium Constants with Temperature (Van't Hoff Equation)
or
Chemical Equilibria
 "extent of reaction" parameter,

corresponds to reaction advancement from reactant to products
 For a substance with several phases in equilibrium, the chemical potentials of all present phases are equal (e.g. the chemical potentials of the vapor and the liquid are equal)
 For ideal solutions every component has its chemical potential given by
Clapeyron Equation
ClausiusClapeyron Equation
or
This can be rewritten as:
Maxwell Relations
Other Concepts
 Definitions of chemical potential, activity, fugacity, activity coefficient
 "Regular" solution model for nonelectrolytes
 Colligative properties
 Variations of equilibrium constants with pressure
 Gibbs phase rule
 Phase equilibrium, constructions of phase diagrams for a singlecomponent system
 Triple points on a phase diagram … points on phase diagrams where three phases are in equilibrium
Relevant pages in Mortimer are Chapters 6, 7, 8, and Chapter 5 (starting with Section 5.3).
Electrolyte chemistry will NOT be on Exam #2.
Note: This list is only a guide to help you study. It is NOT comprehensive, and the exam may cover any topics discussed in class. Please remember also that even though Exam #2 will cover primarily the material discussed after Exam #1, all exams are comprehensive and you may need to know some concepts covered on Exam #1, especially material that relates directly to current topics (e.g. calculations of DG, DS, DH, DA, heat capacities, etc).
