electromotive force

Examples of electromotive force in the following topics:

• The Nernst Equation

  • It can also be used to determine the total voltage, or electromotive force, for a full electrochemical cell.
  • The Nernst equation gives a formula that relates the electromotive force of a nonstandard cell to the concentrations of species in solution:
  • First, find the electromotive force for the standard cell, which assumes concentrations of 1 M.

• Equilibrium Constant and Cell Potential

  • It can also be used to determine the total voltage, or electromotive force, for a full electrochemical cell.

• Dispersion Force

  • These intermolecular forces are also sometimes called "induced dipole-induced dipole" or "momentary dipole" forces.
  • London dispersion forces are part of the van der Waals forces, or weak intermolecular attractions.
  • Van der Waals forces help explain how nitrogen can be liquefied.
  • London dispersion forces allow otherwise non-polar molecules to have attractive forces.
  • There are two kinds of attractive forces shown in this model: Coulomb forces (the attraction between ions) and Van der Waals forces (an additional attractive force between all atoms).

• Ion-Dipole Force

  • The ion-dipole force is an intermolecular attraction between an ion and a polar molecule.
  • However, ion-dipole forces involve ions instead of solely polar molecules.
  • Ion-dipole forces are stronger than dipole interactions because the charge of any ion is much greater than the charge of a dipole; the strength of the ion-dipole force is proportionate to ion charge.
  • An ion-induced dipole force occurs when an ion interacts with a non-polar molecule.
  • Ion-dipole forces are generated between polar water molecules and a sodium ion.

• Predicting if a Metal Will Dissolve in Acid

  • This sequence is known as the electromotive, or activity, series of the metals.

• The Effect of Intermolecular Forces

  • At high pressures and low temperatures, intermolecular forces between gas particles can cause significant deviation from ideal behavior.
  • Intermolecular forces describe the attraction and repulsion between particles.
  • At high pressures, gas particles are forced into close proximity with one another, causing significant intermolecular interactions.
  • When the weight of individual gas molecules becomes significant, London dispersion forces, or instantaneous dipole forces, tend to increase, because as molecular weight increases, the number of electrons within each gas molecule tends to increase as well.
  • At high pressures and low temperatures, these attractive forces can become significant.

• Nuclear Fusion

  • The origin of the energy released in fusion of light elements is due to an interplay of two opposing forces: the nuclear force that draws together protons and neutrons, and the Coulomb force that causes protons to repel each other.
  • This force, called the strong nuclear force, overcomes electric repulsion in a very close range.
  • The effect of nuclear force is not observed outside the nucleus, hence the force has a strong dependence on distance; it a short-range force.
  • When a nucleon is added to a nucleus, the nuclear force attracts it to other nucleons, but primarily to its immediate neighbors due to the short range of the force.
  • At nucleus radii distances, the attractive nuclear force is stronger than the repulsive electrostatic force.

• Capillary Action

  • The molecules in any sample of matter experience intermolecular forces, which are attractive or repulsive forces between atoms or molecules within the sample.
  • When attractive forces occur between like molecules, they are referred to as cohesive forces, or resulting in cohesion, because they hold the molecules of sample close together.
  • It occurs when the intermolecular attractive forces between the liquid and the solid surrounding surfaces (adhesive forces) are stronger than the cohesive forces within the liquid.
  • Adhesion forces between the fluid and the solid inner wall pull the liquid column up until there is a sufficient mass of liquid for gravitational forces to counteract these forces.
  • The curvature of the surface at the top of a column of fluid in a narrow tube is caused by the relative strength of the forces responsible for the surface tension of the fluid (cohesive forces) and the adhesive forces to the walls of the container.

• Surface Tension

  • Therefore, the cohesive forces result in the phenomenon of surface tension.
  • If no force acts normal (perpendicular) to a tensioned surface, the surface must remain flat.
  • In order for the surface tension forces to cancel out this force due to pressure, the surface must be curved.
  • For a needle floating on the surface of a liquid, the downward force of the needle's weight is balanced by the upward forces of surface tension from the liquid. 
  • Note that the forces from the surface tension are symmetrical.

• Introduction to Intermolecular Forces

  • This attractive force has its origin in the electrostatic attraction of the electrons of one molecule or atom for the nuclei of another.
  • If there were no van der Waals forces, all matter would exist in a gaseous state, and life as we know it would not be possible.
  • It should be noted that there are also smaller repulsive forces between molecules that increase rapidly at very small intermolecular distances.