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The
Internal Energy, U, of a system is an extensive thermodynamic property
that measures the energy stored in a system as a result of its microscopic
structure. The internal energy will include contributions from the thermal,
mechanical, electrical, magnetic, chemical, and surface energies of the
system. The internal energy per unit mass of the system is the specific
internal energy, u.
The
internal energy of a system of constant composition can be changed by work
or heat interactions with its surroundings. Both of these energy transfer
processes are path dependent, however, the internal energy is a function
only of the state of the system. The First Law of thermodynamic connects
these quantities: du = dq
+ dw
, where dn
denotes a path dependent quantity change. If the system considered is adiabatic
so that no heat transfer occurs: du
= dw.
This expression shows that the adiabatic work done in taking a system between
an initial and a final state is path independent. |
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