phase diagram

(noun)

A graph showing the phase a sample of matter has under different conditions of temperature and pressure.

Related Terms

  • T
  • dipole
  • amphoteric
  • equilibrium

Examples of phase diagram in the following topics:

  • Major Features of a Phase Diagram

    • A phase diagram is a graph which shows under what conditions of temperature and pressure distinct phases of matter occur.
    • The simplest phase diagrams are of pure substances.
    • The major features of a phase diagram are phase boundaries and the triple point.
    • The phase diagram for water is useful for learning how to analyze these diagrams.
    • In this phase diagram, which is typical of most substances, the solid lines represent the phase boundaries.
  • Interpreting Phase Diagrams

    • Phase diagrams illustrate the effects selected variables of a system have on the state of matter.
    • Phase diagrams illustrate the effects selected variables of a system have on the state of matter.
    • When evaluating the phase diagram, it is worth noting that the solid-liquid phase boundary in the phase diagram of most substances has a positive slope.
    • With a knowledge of the major components of phase diagrams and the features of phase plots, a phase diagram can be used to understand how altering thermodynamic parameters influences the states/phases of matter a sample of a substance is in.
    • A typical phase diagram illustrating the major components of a phase diagram as well as the critical point.
  • Solid to Gas Phase Transition

    • Sublimation is the phase transition from the solid to the gaseous phase, without passing through an intermediate liquid phase.
    • Sublimation is the process of transformation directly from the solid phase to the gaseous phase, without passing through an intermediate liquid phase.
    • It is an endothermic phase transition that occurs at temperatures and pressures below a substance's triple point (the temperature and pressure at which all three phases coexist) in its phase diagram.
    • But at temperatures below that of the triple point, a decrease in pressure will result in a phase transition directly from the solid to the gaseous.
    • At temperatures and pressures below those of the triple point, a phase change between the solid and gas phases can take place.
  • Aluminosilicates

    • The phase diagram of Al2SiO5 showing its different forms (called "polymorphs").
  • Supercritical Fluids

    • In the pressure-temperature phase diagram of CO2, the boiling separates the gas and liquid region and ends in the critical point, where the liquid and gas phases disappear to become a single supercritical phase.
    • The system consists of 2 phases in equilibrium, a dense liquid and a low density gas.
    • At the critical point, (304.1 K and 7.38 MPa) there is no difference in density, and the two phases become one fluid phase.
    • The dry ice melts under high pressure, and forms a liquid and gas phase.
    • When the vessel is heated, the CO2 becomes supercritical -- meaning the liquid and gas phases merge together into a new phase that has properties of a gas, but the density of a liquid.
  • The Structure and Properties of Water

    • Its liquid phase, the most common phase of water on Earth, is the form that is generally meant by the word "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.
    • Phase diagrams help describe how water changes states depending on the pressure and temperature.
    • During the phase transition between two phases (i.e, along these boundaries), the phases are in equilibrium with each other.
    • The three phases of water – liquid, solid, and vapor – are shown in temperature-pressure space.
  • Crystalline Solids

    • However, if the solid melts, or the liquid freezes, a discontinuity occurs and the temperature of the sample remains constant until the phase change is complete.
    • This behavior is shown in the diagram below, with the green segment representing the solid phase, light blue the liquid, and red the temperature invariant liquid/solid equilibrium.
    • The phase diagram below shows the melting point behavior of mixtures ranging from pure A on the left to pure B on the right.
    • Such a species usually has a sharp congruent melting point and produces a phase diagram having the appearance of two adjacent eutectic diagrams.
    • The A:B complex has a melting point of 54 ºC, and the phase diagram displays two eutectic points, the first at 50 ºC, the second at 30 ºC.
  • Bond Order

    • This MO diagram depicts the molecule H2, with the contributing AOs on the outside sandwiching the MO.
    • The third diagram hypothesizes the molecule dihelium (He2).
    • However, removing an electron from the antibonding level produces the molecule He2+, which is stable in the gas phase with a bond order of 0.5.
    • The last diagram presents the molecule dilithium (Li2).
    • The molecule Li2 is a stable molecule in the gas phase, with a bond order of one.
  • Theoretical Models for Pericyclic Reactions

    • The simple compound ethene is made up of six atoms held together by six covalent bonds, as described in the first diagram below.
    • In the case of ethene and other isolated double bonds, descriptions of the localized π orbitals are displayed in the second diagram above.
    • Several important characteristics of molecular orbitals need to be pointed out, and this diagram will serve to illustrate them.
    • This phase change is sometimes designated by plus and minus signs associated with discrete regions of the orbital, but this notation may sometimes be confused for an electric charge.
    • In the second diagram above, regions having one phase sign are colored blue, while those having an opposite sign are colored red.
  • Bonding and Antibonding Molecular Orbitals

    • Bonding and antibonding orbitals are illustrated in MO diagrams, and are useful for predicting the strength and existence of chemical bonds.
    • Two atomic orbitals can overlap in two ways, depending on their phase relationship.
    • An orbital's phase is a direct consequence of electrons' wave-like properties.
    • If the phase changes, the bond becomes a pi bond (π-bond).
    • The next step in constructing an MO diagram is filling the newly formed molecular orbitals with electrons.
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