chemical potential

Examples of chemical potential in the following topics:

• Equilibrium Constant and Cell Potential

  • Each chemical species has an electrochemical potential (quantity with units of energy) at any given location, which represents how easy or difficult it is to add more of that species to that location.
  • If possible, a species will move from areas with higher electrochemical potential to areas with lower electrochemical potential.
  • We say the ions have electric potential energy, and are moving to lower their potential energy.
  • We say that the sugar molecules have a "chemical potential," which is higher in the high-concentration areas, and the molecules move to lower their chemical potential.
  • These two examples show that an electrical potential and a chemical potential can both give the same result: a redistribution of the chemical species.

• Postsynaptic Potentials and Their Integration at the Synapse

  • Postsynaptic potentials are excitatory or inhibitory changes in the graded membrane potential in the postsynaptic terminal of a chemical synapse.
  • Postsynaptic potentials are changes in the membrane potential of the postsynaptic terminal of a chemical synapse.
  • This converts a chemical signal into an electrical signal.
  • Chemical synapses are either excitatory or inhibitory depending on how they affect the membrane potential of the postsynaptic neuron.
  • Unlike the action potential in axonal membranes, chemically-gated ion channels open on postsynaptic membranes.

• Types of Energy

  • The various types of energy include kinetic, potential, and chemical energy.
  • On a chemical level, the bonds that hold the atoms of molecules together have potential energy.
  • This type of potential energy is called chemical energy, and like all potential energy, it can be used to do work.
  • The potential energy stored within chemical bonds can be harnessed to perform work for biological processes.
  • The molecules in gasoline (octane, the chemical formula shown) contain chemical energy.

• Standard Reduction Potentials

  • Reduction potential (also known as redox potential, oxidation/reduction potential, or Eh) measures the tendency of a chemical species to acquire electrons and thereby be reduced.
  • Reduction potential is measured in volts (V) or millivolts (mV).
  • Each species has its own intrinsic reduction potential.
  • Historically, many countries, including the United States and Canada, used standard oxidation potentials rather than reduction potentials in their calculations.
  • However, because these can also be referred to as "redox potentials," the terms "reduction potentials" and "oxidation potentials" are preferred by the IUPAC.

• Mechanics of the Action Potential

  • During a chemical reaction, a chemical called a neurotransmitter is released from one cell into another.
  • Resting potential.
  • If the membrane potential reaches -55 mV, it has reached the threshold of excitation.
  • Eventually, the cell potential reaches +40 mV, or the action potential.
  • This expulsion acts to restore the localized negative membrane potential of the cell.

• Synaptic Transmission

  • In a chemical synapse, the pre and post synaptic membranes are separated by a synaptic cleft, a fluid filled space.
  • Neurotransmission at a chemical synapse begins with the arrival of an action potential at the presynaptic axon terminal.
  • When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated Na+ channels.
  • As long as it is bound to a post synaptic receptor, a neurotransmitter continues to affect membrane potential.
  • Communication at chemical synapses requires release of neurotransmitters.

• Concentration of Cells

  • The standard potential of an electrochemical cell requires standard conditions for all of the reactants.
  • When reactant concentrations differ from standard conditions, the cell potential will deviate from the standard potential.
  • In the late 19th century, Josiah Willard Gibbs formulated a theory to predict whether a chemical reaction would be spontaneous based on free energy:
  • In chemistry, a reaction quotient is a function of the activities or concentrations of the chemical species involved in a chemical reaction.
  • Discuss the implications of the Nernst equation on the electrochemical potential of a cell

• Nerve Impulse Transmission within a Neuron: Action Potential

  • A neuron can receive input from other neurons via a chemical called a neurotransmitter.
  • The action potential travels down the neuron as Na+ channels open.
  • Action potentials are considered an "all-or nothing" event.
  • The diffusion of K+ out of the cell hyperpolarizes the cell, making the membrane potential more negative than the cell's normal resting potential.
  • At this point, the sodium channels return to their resting state, ready to open again if the membrane potential again exceeds the threshold potential.

• Neurotransmitters

  • Neurotransmitters are chemicals that transmit signals from a neuron across a synapse to a target cell.
  • Inhibitory neurotransmitters cause hyperpolarization of the postsynaptic cell (that is, decreasing the voltage gradient of the cell, thus bringing it further away from an action potential), while excitatory neurotransmitters cause depolarization (bringing it closer to an action potential).
  • The following groups refer to the specific chemicals, and within the groups are specific systems, some of which block other chemicals from entering the cell and some of which permit the entrance of chemicals that were blocked before.
  • Muscarine, a chemical product of certain mushrooms, binds to the muscarinic receptor.
  • The depolarizing (more likely to reach an action potential) or hyperpolarizing (less likely to reach an action potential) effect is also dependent on the receptor.

• Effective Disinfection

  • Most disinfectants, however, are by nature, potentially harmful (even toxic) to humans or animals.
  • Those that are used indoors should never be mixed with other cleaning products, or else chemical reactions can occur.
  • Should some bacteria survive a chemical attack, they give rise to new generations composed completely of bacteria that are resistant to the particular chemical used.
  • Under a sustained chemical attack, the surviving bacteria in successive generations are increasingly resistant to the chemical used, and ultimately the chemical is rendered ineffective.
  • Low-level disinfection kills some viruses and bacteria with a chemical germicide registered as a hospital disinfectant by the EPA.