5 Thermodynamic properties
The behavior of the system depends upon the interaction of energy with
or without mass transfer across the boundary. Every system has certain
characteristics by which its physical conditions may be described. Such be-
havior/characteristics of a system are called the properties of the system.
There are 8 (eight) properties describing the behavior of a system. They
are pressure, temperature, volume, entropy, internal energy, enthalpy, Gibbs
function and Helmholtz functions. Pressure, temperature and volume are
measurable properties and they are also known as physical properties (also
known as macroscopic properties). Other properties are derived properties
(they can not be measured directly). In sense of thermodynamics, pressure is
always expressed in terms of absolute pressure and temperature is expressed
in Kelvin.
5.1 Intensive and extensive properties
Thermodynamic properties can be divided into 2 (two) general classes such
as intensive and extensive properties. An intensive property, is a physical
property of a system that does not depend on the system size or the amount
of material in the system. By contrast, an extensive property of a system
does depend on the system size or the amount of material in the system.
According to the definitions, density, pressure and temperature are intensive
properties and volume, internal energy are extensive properties.
Extensive properties are symbolized by upper case (capital) letter such
as V (volume), KE (kinetic energy), PE (potential energy), etc. Intensive
properties are symbolized by lower case letters such as v (specific volume), u
(specific internal energy), h (specific enthalpy), etc.
A specific property is the intensive property obtained by dividing an ex-
tensive property of a system by its mass. For example, heat capacity is an
extensive property of a system. For example, the ratio of an object’s vol-
ume and mass, which are two extensive properties, is specific volume (v) ,
which is an intensive property. When the extensive property is represented
by an upper-case letter, the symbol for the corresponding intensive property
is usually represented by a lower-case letter.
Exceptions: Temperature (intensive), mass (extensive), and number of
moles (extensive). The use of symbols for temperature, mass and moles are
traditional.
4
, 6 State
A thermodynamic state of a system is its condition at a specific time and
is defined by specifying values of a set of measurable properties sufficient
to determine all other properties. For fluid systems, typical properties are
pressure, volume and temperature. More complex systems may require the
specification of more unusual properties. As an example, the state of an
electric battery requires the specification of the amount of electric charge it
contains. State of a thermodynamic system can be indicated in a diagram
with properties as coordinates.
7 Process
A process is a change in the state of the system over time, starting with
a definite initial state and ending with a definite final state. The process
is defined by a path, which is the continuous sequence of consecutive states
through which the system passes, including the initial state, the intermediate
states, and the final state. The process has a direction along the path. The
path could be described by a curve in an N -dimensional space in which each
coordinate axis represents one of the N independent variables.
Expansion is a process in which the system volume increases; in com-
pression, the volume decreases. An isothermal process is one in which
the temperature of the system remains uniform and constant. An isobaric
or isopiestic process refers to uniform constant pressure, and an isochoric
process refers to constant volume. An adiabatic process is one in which there
is no heat transfer across any portion of the boundary.
7.1 Cyclic process
A cyclic process is a process in which the state of the system changes and then
returns to the initial state. Therefore, state properties such as temperature,
pressure, volume, and internal energy of the system do not change over a
complete cycle.
7.2 Quasi-static Process
A quasi-static process (also known as quasi-equilibrium, from the Latin
quasi, meaning ’as if ’ ), is a thermodynamic process that happens slowly
enough for the system to remain in internal equilibrium. An example of this
is quasi-static compression, where the volume of a system changes at a rate
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The behavior of the system depends upon the interaction of energy with
or without mass transfer across the boundary. Every system has certain
characteristics by which its physical conditions may be described. Such be-
havior/characteristics of a system are called the properties of the system.
There are 8 (eight) properties describing the behavior of a system. They
are pressure, temperature, volume, entropy, internal energy, enthalpy, Gibbs
function and Helmholtz functions. Pressure, temperature and volume are
measurable properties and they are also known as physical properties (also
known as macroscopic properties). Other properties are derived properties
(they can not be measured directly). In sense of thermodynamics, pressure is
always expressed in terms of absolute pressure and temperature is expressed
in Kelvin.
5.1 Intensive and extensive properties
Thermodynamic properties can be divided into 2 (two) general classes such
as intensive and extensive properties. An intensive property, is a physical
property of a system that does not depend on the system size or the amount
of material in the system. By contrast, an extensive property of a system
does depend on the system size or the amount of material in the system.
According to the definitions, density, pressure and temperature are intensive
properties and volume, internal energy are extensive properties.
Extensive properties are symbolized by upper case (capital) letter such
as V (volume), KE (kinetic energy), PE (potential energy), etc. Intensive
properties are symbolized by lower case letters such as v (specific volume), u
(specific internal energy), h (specific enthalpy), etc.
A specific property is the intensive property obtained by dividing an ex-
tensive property of a system by its mass. For example, heat capacity is an
extensive property of a system. For example, the ratio of an object’s vol-
ume and mass, which are two extensive properties, is specific volume (v) ,
which is an intensive property. When the extensive property is represented
by an upper-case letter, the symbol for the corresponding intensive property
is usually represented by a lower-case letter.
Exceptions: Temperature (intensive), mass (extensive), and number of
moles (extensive). The use of symbols for temperature, mass and moles are
traditional.
4
, 6 State
A thermodynamic state of a system is its condition at a specific time and
is defined by specifying values of a set of measurable properties sufficient
to determine all other properties. For fluid systems, typical properties are
pressure, volume and temperature. More complex systems may require the
specification of more unusual properties. As an example, the state of an
electric battery requires the specification of the amount of electric charge it
contains. State of a thermodynamic system can be indicated in a diagram
with properties as coordinates.
7 Process
A process is a change in the state of the system over time, starting with
a definite initial state and ending with a definite final state. The process
is defined by a path, which is the continuous sequence of consecutive states
through which the system passes, including the initial state, the intermediate
states, and the final state. The process has a direction along the path. The
path could be described by a curve in an N -dimensional space in which each
coordinate axis represents one of the N independent variables.
Expansion is a process in which the system volume increases; in com-
pression, the volume decreases. An isothermal process is one in which
the temperature of the system remains uniform and constant. An isobaric
or isopiestic process refers to uniform constant pressure, and an isochoric
process refers to constant volume. An adiabatic process is one in which there
is no heat transfer across any portion of the boundary.
7.1 Cyclic process
A cyclic process is a process in which the state of the system changes and then
returns to the initial state. Therefore, state properties such as temperature,
pressure, volume, and internal energy of the system do not change over a
complete cycle.
7.2 Quasi-static Process
A quasi-static process (also known as quasi-equilibrium, from the Latin
quasi, meaning ’as if ’ ), is a thermodynamic process that happens slowly
enough for the system to remain in internal equilibrium. An example of this
is quasi-static compression, where the volume of a system changes at a rate
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