critical

(adjective)

Of the point (in temperature, reagent concentration etc. ) where a nuclear or chemical reaction becomes self-sustaining.

Related Terms

Examples of critical in the following topics:

  • Supercritical Fluids

    • The critical properties of some substances used as solvents and as supercritical fluids are shown in Table 1.
    • However, close to the critical point, the density can drop sharply with a slight increase in temperature.
    • The critical point of a binary mixture can be estimated as the arithmetic mean of the critical temperatures and pressures of the two components,
    • Thus, above the critical temperature a gas cannot be liquified by pressure.
    • At slightly above the critical temperature (310 K), in the vicinity of the critical pressure, the line is almost vertical.

  • Interpreting Phase Diagrams

    • Phase diagrams can also be used to explain the behavior of a pure sample of matter at the critical point.
    • The critical point, which occurs at critical pressure (Pcr) and critical temperature (Tcr), is a feature that indicates the point in thermodynamic parameter space at which the liquid and gaseous states of the substance being evaluated are indistinguishable.
    • At temperatures above the critical temperature, the kinetic energy of the molecules is high enough so that even at high pressures the sample cannot condense into the liquid phase.
    • A typical phase diagram illustrating the major components of a phase diagram as well as the critical point.

  • Three States of Matter

    • The highest temperature at which a particular liquid can exist is called its critical temperature.
    • A gas at a temperature below its critical temperature can also be called a vapor.
    • A supercritical fluid (SCF) is a gas whose temperature and pressure are greater than the critical temperature and critical pressure.

  • 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."
    • Most nuclear reactors include a "starter" neutron source that ensures a few free neutrons in the reactor core, so a chain reaction will occur immediately when the core is made critical.

  • The Structure and Properties of Water

    • When water achieves a specific critical temperature and a specific critical pressure (647 K and 22.064 MPa), the liquid and gas phases merge into one homogeneous fluid phase that shares properties of both gas and liquid.

  • Acute Radiation Damage

    • This might be the result of a nuclear explosion, a criticality accident, a radiotherapy accident, escape of radioactive waste, human error in a nuclear reactor, etc.

  • The Atomic Bomb

    • This is accomplished either by shooting one piece of sub-critical material into another, termed the "gun" method, or by compressing a sub-critical sphere of material using chemical explosives to many times its original density, called the "implosion" method.

  • Boiling & Melting Points

    • Molecular size is important, but shape is also critical, since individual molecules need to fit together cooperatively for the attractive lattice forces to be large.

  • The Arndt-Eistert Reaction

    • This rearrangement is a critical step in the Arndt-Eistert procedure for elongating a carboxylic acid by a single methylene unit, as described in the diagram below.

  • Synthesis of Amino Acids

    • The structure of this amine is not shown, because it is not a critical factor in the logical progression of steps.