electrochemical cell

Examples of electrochemical cell in the following topics:

• The Nernst Equation

  • In electrochemistry, the Nernst equation can be used to determine the reduction potential of an electrochemical cell.
  • In electrochemistry, the Nernst equation can be used, in conjunction with other information, to determine the reduction potential of a half-cell in an electrochemical cell.
  • It can also be used to determine the total voltage, or electromotive force, for a full electrochemical cell.
  • Find the cell potential of a galvanic cell based on the following reduction half-reactions where [Ni2+] = 0.030 M and [Pb2+] = 0.300 M.
  • The added half-reactions with the adjusted E0 cell are:

• Concentration of Cells

  • Walther Nernst proposed a mathematical model to determine the effect of reactant concentration on the electrochemical cell potential.
  • The standard potential of an electrochemical cell requires standard conditions for all of the reactants.
  • The change in Gibbs free energy for an electrochemical cell can be related to the cell potential.
  • Under standard conditions, the output of this pair of half-cells is well known.
  • Discuss the implications of the Nernst equation on the electrochemical potential of a cell

• Free Energy and Cell Potential

  • The basis for an electrochemical cell, such as the galvanic cell, is always a redox reaction that can be broken down into two half-reactions: oxidation occurs at the anode, where there is a loss of electrons, and reduction occurs at the cathode, where there is a gain of electrons.
  • This is the opposite of the cell potential, which is positive when electrons flow spontaneously through the electrochemical cell.
  • Calculate the change in Gibbs free energy of an electrochemical cell where the following redox reaction is taking place:
  • A demonstration electrochemical cell setup resembling the Daniell cell.
  • Calculate the change in Gibbs free energy of an electrochemical cell, and discuss its implications for whether a redox reaction will be spontaneous

• Electrochemical Cell Notation

  • Cell notation is shorthand that expresses a certain reaction in an electrochemical cell.
  • Cell notations are a shorthand description of voltaic or galvanic (spontaneous) cells.
  • The anode half-cell is described first; the cathode half-cell follows.
  • A typical arrangement of half-cells linked to form a galvanic cell.
  • Produce the appropriate electrochemical cell notation for a given electrochemical reaction

• Electrochemical Gradient

  • To move substances against the membrane's electrochemical gradient, the cell utilizes active transport, which requires energy from ATP.
  • To move substances against a concentration or electrochemical gradient, the cell must use energy.
  • Active transport mechanisms, collectively called pumps, work against electrochemical gradients.
  • Electrochemical gradients arise from the combined effects of concentration gradients and electrical gradients.
  • Define an electrochemical gradient and describe how a cell moves substances against this gradient

• Primary Active Transport

  • The sodium-potassium pump maintains the electrochemical gradient of living cells by moving sodium in and potassium out of the cell.
  • One of the most important pumps in animals cells is the sodium-potassium pump (Na+-K+ ATPase), which maintains the electrochemical gradient (and the correct concentrations of Na+ and K+) in living cells.
  • The sodium-potassium pump moves two K+ into the cell while moving three Na+ out of the cell.
  • Primary active transport moves ions across a membrane, creating an electrochemical gradient (electrogenic transport).
  • Describe how a cell moves sodium and potassium out of and into the cell against its electrochemical gradient

• Equilibrium Constant and Cell Potential

  • If possible, a species will move from areas with higher electrochemical potential to areas with lower electrochemical potential.
  • In equilibrium, the electrochemical potential will be constant everywhere for each species.
  • It can also be used to determine the total voltage, or electromotive force, for a full electrochemical cell.
  • The cell equilibrium constant, K, can be derived from the Nernst equation:
  • Schematic of a galvanic cell for the reaction between Zn and Cu.

• Chemiosmosis and Oxidative Phosphorylation

  • Chemiosmosis is the movement of ions across a selectively permeable membrane, down their electrochemical gradient.
  • The electrons cause conformation changes in the shapes of the proteins to pump H+ across a selectively permeable cell membrane.  
  • The uneven distribution of H+ ions across the membrane establishes both concentration and electrical gradients (thus, an electrochemical gradient) owing to the hydrogen ions' positive charge and their aggregation on one side of the membrane.
  • If the membrane were open to diffusion by the hydrogen ions, the ions would tend to spontaneously diffuse back across into the matrix, driven by their electrochemical gradient.
  • This protein acts as a tiny generator turned by the force of the hydrogen ions diffusing through it, down their electrochemical gradient.

• Proton Reduction

  • In animal cells, the mitochondria performs similar functions.
  • An electrochemical gradient has two components.
  • The membrane in question is the inner mitochondrial membrane in eukaryotes and the cell membrane in prokaryotes.
  • Proton reduction is important for setting up electrochemical gradients for anaerobic respiration.
  • In contrast, fermentation does not utilize an electrochemical gradient.

• Secondary Active Transport

  • In secondary active transport, a molecule is moved down its electrochemical gradient as another is moved up its concentration gradient.
  • Instead, another molecule is moved up its concentration gradient, which generates an electrochemical gradient.
  • The molecule of interest is then transported down the electrochemical gradient.
  • Secondary active transport brings sodium ions, and possibly other compounds, into the cell.
  • Many amino acids, as well as glucose, enter a cell this way.