Specific Energy

Specific energy is defined as the energy per unit mass. Common metric units are J/kg. It is an intensive property. Contrast this with energy, which is an extensive property. There are two main types of specific energy: potential energy and specific kinetic energy. Others are the gray and sievert, measures for the absorption of radiation. The concept of specific energy applies to a particular or theoretical way of extracting useful energy from the material considered that is usually implied by context.

Thermodynamic properties related to specific energy include specific internal energy, specific enthalpy, specific Gibbs free energy, and specific Helmholtz free energy, all of which use units of energy per mass such as J/kg. These intensive properties are each symbolized by using the lower case letter of the symbol for the corresponding extensive property, which is symbolized by a capital letter. For example, the extensive thermodynamic property enthalpy is symbolized by H; specific enthalpy is symbolized by h.

If a defined chemical compound is used which has a definite molar mass, such intensive thermodynamic properties can be expressed on a per mole basis instead of a per mass basis. Such quantities can be described as molar quantities; for example, molar enthalpy meaning enthalpy per mole. These intensive quantities will use units of energy per mole, such as J/mol (mol is short for mole) or in older chemistry literature kcal/mol.

By dividing by 3.6 the figures for megajoules per kilogram can be converted to kilowatt-hours per kilogram. Unfortunately, the useful energy available by extraction from an energy store is always less than the energy put into the energy store, as explained by the laws of thermodynamics.

Read more about Specific Energy:  Energy Density of Food, Astrodynamics, Miscellaneous

Other articles related to "energy, specific energy":

Oberth Effect - Description
... acting on a fixed object, as in a static firing, does no useful work at all the rocket's stored energy is entirely expended on accelerating its propellant to hypersonic speed ... through a distance is the definition of mechanical energy or work ... the faster they move), the greater the kinetic energy imparted to the rocket and its payload and the less to its exhaust ...
Aircraft Specific Energy - Applications
... made use of the concept since the 1950s in the form of energy analysis ... In this approach, the specific energy is defined as one of the dynamic states of the problem and is the slowest varying state ... as altitude and flight path angle are approximated as infinitely fast compared to the specific energy dynamics ...
Specific Energy - Miscellaneous
... Kinetic energy per unit mass 1/2v2, where v is the speed (giving J/kg when v is in m/s) ... See also kinetic energy per unit mass of projectiles ... Potential energy with respect to gravity, close to earth, per unit mass gh, where g is the acceleration due to gravity (standardized as ~9.8 m/s2) and h is the height above the reference level ...

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