ABSTRACT

This chapter treats forces other than pressures in pistons. The chapter introduces Maxwell's relations, which give insights about those forces. Maxwell's relations are relationships between partial derivatives. These relations gives us hard-to-measure quantities of interest from properties that are easy to measure. Cell membranes are composed of two opposing monolayers of lipid molecules. Lipid bilayers and monolayers have an ability to change their surface area per lipid molecule, A, even when temperature, pressure, and the numbers of molecules are fixed. A lipid bilayer adjusts its area to have an equilibrium area per molecule, that minimizes the free energy function G(A). The chapter uses partial molar quantities to show that pV effects are typically small in liquids and solids. For condensed phases, we can use Gibbs or Helmholtz free energies interchangeably. For many condensed-phase properties, Gibbs and Helmholtz free energies are interchangeable.