1. Composition Dependence of ΔG (6.3-6.4) For a mixture, the Gibbs energy also depends on the composition of the mixture – The dependence on the change in molar quantities of a component is referred to as the chemical potential (μ i ) Chemical potential dictates in which direction components will move in a mixture – Components will move from regions of high chemical potential to low chemical potential until the potentials are equivalent throughout the sample

2. Ion Transport Across Membranes (10.4) Transport of species across a membrane can be endergonic or exergonic – Passive transport (exergonic) occurs when a species diffuses across a membrane from high concentration to low concentration – Active transport (endergonic) occurs when a species diffuses across a membrane from low concentration to high concentration – Energetics are related to chemical potential on both sides of the membrane For charged species, the chemical potential is modified to an electrochemical potential – Electrochemical potential depends on charge of species and the electric potential Transport of charged species depends on concentration differences and on electric potential across the membrane – At equilibrium, the electric potential can be related to the concentration gradient

3. Donnan Potential (9.13) A potential can develop when a semi-permeable membrane is used to separate permeable species to impermeable speciessemi-permeable membrane – Small inorganic ions (e.g., Na + and Cl - ) may pass through the membrane, while large macromolecules (e.g., proteins) may not – If the macromolecule is charged and its counterion is found on both sides of the membrane, an equilibrium must be established based on chemical potential For two compartments separated by a semi-permeable membrane, transport of ions will occur under two conditions – Chemical potential of each permeable species tries to equilibrate (i.e., approach equal concentrations) – For every cation transported, an anion must accompany it (electrical neutrality) The impermeable species forces the concentrations of the permeable species to be unequal on both sides of membrane – Donnan potential is a measure of how far the ratio between permeable species on each side of the membrane deviates from one

4. Donnan Potential