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Composition Dependence of ΔG (6.3-6.4)

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 )

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Composition Dependence of ΔG (6.3-6.4)

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  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 (μi) • 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 species • 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

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