This chapter looks at how changes in composition affect chemical potential, and this properties such as vapor pressure, boiling and freezing points, and osmotic pressure. We will also explore a convenient means of describing solutions that deviate from ideal behavior by introducting the concept of activity. A simple electrolyte solution model (Debey-Huckel theory) is also briefly discussed.
The maximum solubility of a solute is determined by the equality of the chemical potentials of the dissolved and undissolved forms. Students will learn how this equilibrium condition can be used to estimate solubilities and predict how solubility changes with temperature.
Dissolved solutes lower the chemical potential of a solvent. Students will learn how this effect arises and how it serves as the thermodynamic basis for many of the characteristic properties of solutions.
The lowering of solvent chemical potential alters the temperatures at which phase transitions occur. Students will derive and apply expressions for freezing-point depression and boiling-point elevation using cryoscopic and ebullioscopic constants.
The composition of a solution influences the vapor pressure of the solvent. Students will derive and apply Raoult's Law and use it to analyze liquid-vapor equilibrium in ideal solutions.
Henry's Law describes how the vapor pressure of a volitile solute behaves as a function of the solute concentration. It also can be used to predict the maximum solubility of the gas given its partial pressure above the solution.
Osmosis occurs because of differences in chemical potential across a semi-permeable membrane. Students will learn how osmotic pressure arises and apply thermodynamic relationships to calculate osmotic pressures and molar masses.
Real solutions often deviate from ideal behavior. Students will learn how activity and activity coefficients provide corrections that allow ideal solution models to be extended to real systems.
Electrostatic interactions strongly influence the behavior of ionic solutions. Students will learn how ionic strength affects activity coefficients and use the Debye-Hückel equation to estimate deviations from ideal behavior in electrolyte solutions.