Ch20 Lecture

7/24/2019 Ch20 Lecture

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Besides the thermodynamic variables that originally identify a thermodynamic

state of a system, the system is characterized by further quantities called state

functions, which are also called state variables, thermodynamic variables, state

quantities, or functions of state. They are uniquely determined by the

thermodynamic state as it has been identified by the original state variables. A

passage from a given initial thermodynamic state to a given finalthermodynamic state of a thermodynamic system is known as a

thermodynamic process; it typically involve transfers of matter or energy

between system and surroundings. In any thermodynamic process, whatever

may be the intermediate conditions during the passage, the total respective

change in the value of each thermodynamic state variable depends only on the

initial and final states. For an idealized continuousprocess, this means that

infinitesimal incremental changes in such variables are exact differentials.

Together, the incremental changes throughout the process, and the initial and

final states, fully determine the idealized process.

In the most commonly cited simple example, an ideal gas, the thermodynamicvariables would be any two variables out of the following four: entropy,

pressure, temperature, and volume. Thus the thermodynamic state would range

over a two-dimensional state space. The remaining two variables, as well as

other quantities such as the internal energy, would be expressed as state

functions of these two variables. The state functions satisfy certain universal

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Ch20 Lecture

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