phase

Examples of phase in the following topics:

• Interpreting Phase Diagrams

  • The lines that separate these single phase regions are known as phase boundaries.
  • By focusing attention on distinct single phase regions, phase diagrams help us to understand the range over which a particular pure sample of matter exists as a particular phase.
  • 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.

• 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.
  • Phase boundaries, or lines of equilibrium, are boundaries that indicate the conditions under which two phases of matter can coexist at equilibrium.
  • In this phase diagram, which is typical of most substances, the solid lines represent the phase boundaries.

• 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.

• Liquid to Gas Phase Transition

  • Vaporization of a sample of liquid is a phase transition from the liquid phase to the gas phase.
  • Vaporization of a sample of liquid is a phase transition from the liquid phase to the gas phase.
  • This fundamental law of nature is manifested in what is called the "escaping tendency" of the molecules from the phase.
  • Gradually, Pw will rise as molecules escape from the liquid phase and enter the vapor phase.
  • At the same time, some of the vapor molecules will condense back into the liquid phase (step 2).

• 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 Phase of Orbitals

  • One orbital, based on in-phase mixing of the orbitals, will be lower in energy and termed bonding.
  • Two atomic orbitals can overlap in two ways depending on their phase relationship.
  • The phase of an orbital is a direct consequence of the wave-like properties of electrons.
  • If the phase changes, the bond becomes a pi bond (π-bond).
  • The in-phase combination of the s orbitals from the two hydrogen atoms provides a bonding orbital that is filled, whereas the out-of-phase combination provides an anti-bonding orbital that remains unfilled.

• 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.

• Alloys

  • Complete solid solution alloys give single solid phase microstructure.
  • Partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history.
  • Complete solid solution alloys give single solid phase microstructure.
  • Partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history.
  • Alloys can be further classified as homogeneous (consisting of a single phase), heterogeneous (consisting of two or more phases), or intermetallic (where there is no distinct boundary between phases).

• Homogeneous versus Heterogeneous Solution Equilibria

  • The equilibrium constants for reactions that contain substances that are all in the same phase, and reactions that contain substances in different phases, need to be calculated differently.
  • A heterogeneous equilibrium is a system in which reactants and products are found in two or more phases.
  • The phases may be any combination of solid, liquid, or gas phases, and solutions.

• The Kinetic Molecular Theory of Matter

  • The kinetic molecular theory of matter explains how matter can change among the phases of solid, liquid, and gas.
  • An application of the theory is that it helps to explain why matter exists in different phases (solid, liquid, and gas) and how matter can change from one phase to the next.
  • Molecules in the solid phase have the least amount of energy, while gas particles have the greatest amount of energy.
  • A change in phase may occur when the energy of the particles is changed.
  • A change in phase may occur when the energy of the particles is changed.