steady state

Examples of steady state in the following topics:

• Steady-State Approximation

  • The steady state approximation can be used to determine the overall rate law when the rate-determining step is unknown.
  • Both cases can be addressed by using what is known as the steady state approximation.
  • With the steady state assumption, we can write the following:
  • We had no knowledge of the rate-determining step, so we used the steady state approximation for our reaction intermediate, N2O2.
  • Simplify overall rate laws using the steady state approximation for reactions with various or unknown rate-limiting steps, explainting the steady state approximation and when it is valid

• Alkene Isomerization

  • A photochemical reaction occurs when internal conversion and relaxation of an excited state leads to a ground state isomer of the initial substrate molecule, or when an excited state undergoes an intermolecular addition to another reactant molecule in the ground state.
  • Non-radiative internal conversion of this S1 twisted state leads to the transition state region of S0, which decays equally to the ground states of the cis and trans isomers.
  • Molecules occupying this new excited state then relax to either DHP or cis-stilbene ground states.
  • This energetic state then serves to activate a substrate molecule to a lower energy triplet state by collisional exothermic energy and spin exchange, returning the sensitizer to its ground state.
  • The unexpected change in steady state isomer distribution with the triplet energy of the sensitizer could not be rationalized as a single classical energy transfer.

• Mercury Battery

  • Mercury batteries have the advantages of a long shelf life of up to 10 years and steady voltage output.
  • Although these batteries were very common in the mid-20th century, the Mercury-Containing and Rechargeable Battery Management Act (the Battery Act) passed in 1996 in the United States has largely phased out mercury batteries due to environmental concerns.
  • In 1996, the Mercury-Containing and Rechargeable Battery Management Act (the Battery Act; Public law 104-142) was signed into law in the United States.

• The Secondary & Tertiary Structures of DNA

  • In their 1953 announcement of a double helix structure for DNA, Watson and Crick stated, "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.".
  • However, such derivatives of the individual nucleosides are repeatedly synthesized by the cell for a variety of purposes, providing a steady supply of these reagents.

• Environmental Problems Associated with Fossil Fuel Use

  • It shows a steady decrease over time; the September 2010 extent was the third lowest in the satellite record.

• Uses of Oxygen

  • A steady stream of oxygen gas is then produced by the exothermic reaction.

• Ozone Depletion

  • Ozone depletion describes two distinct but related phenomena observed since the late 1970s: (1) a steady decline of about 4 percent per decade in the total volume of ozone in Earth's stratosphere (the ozone layer); and (2) a much larger springtime decrease in stratospheric ozone over Earth's polar regions.

• Nuclear Reactors

  • When a reactor's neutron population remains steady from one generation to the next by creating as many new neutrons as are lost, the fission chain reaction is self-sustaining and the reactor's condition is referred to as "critical."

• Oxidation States

  • The oxidation state of a free element (uncombined element) is zero.
  • For example, Cl- has an oxidation state of -1.
  • When present in most compounds, hydrogen has an oxidation state of +1 and oxygen an oxidation state of −2.
  • As stated in rule number four above, the sum of the oxidation states for all atoms in a molecule or polyatomic ion is equal to the charge of the molecule or ion.
  • This helps determine the oxidation state of any one element in a given molecule or ion, assuming that we know the common oxidation states of all of the other elements.

• Mechanistic Background

  • Both the ground (lowest energy electronic state) and excited states are shown as energy profiles populated by vibrational energy states (green lines) as well as rotational states (not shown).
  • Overall bonding in an excited state is usually lower than in the ground state.
  • The excited state may return to the ground state by emitting a photon (light blue line).
  • Each electronic state will have a group of vibrational (and rotational) states, depicted by light blue lines above each state marker.
  • Such states have a single energy state in an applied magnetic field, and are called singlets.