latent heat of fusion

Examples of latent heat of fusion in the following topics:

• Latent Heat

  • The latent heat is the energy associated with a phase change of a substance.
  • where the latent heat of fusion, Lf, and latent heat of vaporization, Lv, are material constants that are determined experimentally.
  • Latent heat is an intensive property measured in units of J/kg.
  • Lf and Lv are collectively called latent heat coefficients.
  • The long stretches of constant temperature values at 0ºC and 100ºC reflect the large latent heat of melting and vaporization, respectively.

• Liquid to Solid Phase Transition

  • The creation of a nucleus implies the formation of an interface at the boundaries of the new phase.
  • Freezing is almost always an exothermic process, meaning that as liquid changes into solid, heat is released.
  • But heat must be continually removed from the freezing liquid, or the freezing process will stop.
  • The energy released upon freezing, known as the enthalpy of fusion, is a latent heat and is exactly the same as the energy required to melt the same amount of the solid.
  • The amount of heat energy is shown by kinetic energy (KE) shading, with deeper shades of red representing more energetic atoms.

• Fusion Reactors

  • The term "fusion power" is commonly used to refer to potential commercial production of net usable power from a fusion source, similar to the usage of the term "steam power."
  • Heat from the fusion reactions is used to operate a steam turbine which in turn drives electrical generators.
  • The easiest way to do this is to heat the atoms, which has the side effect of stripping their electrons and leaving them as bare nuclei.
  • In most experiments, the nuclei and electrons are left in a fluid known as a plasma, which is a state of matter that occurs when a gas is heated to extreme temperatures.
  • Namely, the heating of the plasma by the products of the fusion reactions must be sufficient to maintain the temperature of the plasma against all losses without external power input.

• Specific Heat and Heat Capacity

  • Heat capacity is a measure of the amount of heat energy required to change the temperature of a pure substance by a given amount.
  • the molar heat capacity, which is the heat capacity per mole of a pure substance.
  • Specific heat capacity is the measure of the heat energy required to raise the temperature of a given quantity of a substance by one kelvin.
  • Latent heat of melting describes tœhe amount of heat required to melt a solid.
  • The above simulation demonstrates the specific heat and the latent heat.

• Nuclear Fusion

  • The fusion of lighter elements in stars releases energy and mass.
  • For example, in the fusion of two hydrogen nuclei to form helium, 0.7 percent of the mass is carried away from the system in the form of kinetic energy or other forms of energy (such as electromagnetic radiation).
  • Research into controlled fusion, with the aim of producing fusion power for the production of electricity, has been conducted for over 60 years.
  • Researchers are working on a reactor that theoretically will deliver 10 times more fusion energy than the amount needed to heat up plasma to required temperatures.
  • Analyze possibility of the use of nuclear fusion for the production of electricity.

• The Hydrogen Bomb

  • The hydrogen bomb is a nuclear weapon that uses a mixture of fission and fusion to produce a massive explosion.
  • A thermonuclear weapon is a nuclear weapon designed to use the heat generated by a fission bomb to compress a nuclear fusion stage.
  • This type of weapon is referred to as a hydrogen bomb, or H-bomb, because it employs hydrogen fusion.
  • The fusion stage in these types of weapons is required in order to efficiently create the large quantities of fission that are characteristic of most thermonuclear weapons.
  • The energy released by the primary section compresses the secondary through a process called "radiation implosion," at which point it is heated and undergoes nuclear fusion.

• Heating Curve for Water

  • A constant rate of heating is assumed, so that one can also think of the x-axis as the amount of time that goes by as a substance is heated.
  • Instead, use the heat of fusion ($\Delta H_{fusion}$ ) to calculate how much heat was involved in that process: $q=m\cdot \Delta H_{fusion}$, where m is the mass of the sample of water.
  • Note that the specific heat capacity of liquid water is different than that of ice.
  • Use the heat of vaporization ($\Delta H_{vap}$ ) to calculate how much heat was absorbed in this process: $q=m\cdot C_{H_2O(g)}\cdot \Delta T$, where m is the mass of the sample of water.
  • Note that the specific heat capacity of gaseous water is different than that of ice or liquid water.

• Calorimetry

  • Calorimetry is the measurement of the heat of chemical reactions or physical changes.
  • Calorimetry is the science of measuring the heat of chemical reactions or physical changes.
  • where δQ is the increment of heat gained by the sample, CV is the heat capacity at constant volume, cv is the specific heat at constant volume, and ΔT is the change in temperature.
  • It does not account for the heat loss through the container or the heat capacity of the thermometer and container itself.
  • The world's first ice-calorimeter, used in the winter of 1782-83, by Antoine Lavoisier and Pierre-Simon Laplace, to determine the heat evolved in variouschemical changes; calculations which were based on Joseph Black's prior discovery of latent heat.

• Convection

  • Example: Calculating Heat Transfer by Convection: Convection of Air Through the Walls of a House.
  • Strategy Heat is used to raise the temperature of air so that Q=mcΔT.
  • The rate of heat transfer is then Q/t, where t is the time for air turnover.
  • The specific heat of air is a weighted average of the specific heats of nitrogen and oxygen, which is c=cp≅1000 J/kg⋅C (note that the specific heat at constant pressure must be used for this process).
  • If the water vapor condenses in liquid droplets as clouds form, heat is released in the atmosphere (this heat release is latent heat)  .

• Animal Viruses

  • Enveloped viruses also have two ways of entering cells after binding to their receptors: receptor-mediated endocytosis and fusion.
  • On the other hand, fusion only occurs with enveloped virions.
  • These viruses, which include HIV among others, use special fusion proteins in their envelopes to cause the envelope to fuse with the plasma membrane of the cell, thus releasing the genome and capsid of the virus into the cell cytoplasm.
  • Under certain conditions, including various types of physical and psychological stress, the latent herpes simplex virus may be reactivated and undergo a lytic replication cycle in the skin, causing the lesions associated with the disease.
  • Latent infections are common with other herpes viruses as well, including the varicella-zoster virus that causes chickenpox.