such transfer of heat or matter can occur. An open system is one that
exchanges both energy and matter with its surroundings. However, if
transfer of energy but not matter is allowed, then we refer to the system as
being closed. The earth is an example of a (nearly) closed system, where
electromagnetic energy is exchanged between the earth and its surroundings but very little matter is exchanged. Actual systems are rarely
completely open or isolated, but can be approximated as such to simplify
the theoretical treatment of the system and distinguish systems with
greatly different degrees of heat or matter transfer. For example, coffee in
even a very well designed thermos (which can be approximated as an
isolated system) will eventually cool to room temperature, but it will
happen far slower than in a paper cup (open system).
Dynamic processes, such as a change in physical state or a chemical
reaction, can be described by the type of interaction that occurs between the
system and the surroundings. If such a process occurs with no heat transfer
between the system and surroundings, we call that process adiabatic.
An isothermal process is one where there is no change in temperature of
the system or the surroundings. A process occurring under conditions of
constant pressure is an isobaric process. Again, these are often ideal situations and, for example, an adiabatic process may in reality occur with a
slight transfer of heat to or from the surroundings, such as when a gas
cylinder becomes cold to the touch when vented rapidly. We use terminology such as open, closed, isolated, isothermal, adiabatic, and isobaric to
carefully define the state of a system and/or delineate the nature of the
process involving the interaction between the system and its surroundings.
2.1.2 Some thermodynamic variables
The thermodynamic state of a system is specified by a set of variables. For
example, the change in the internal energy of a system can be expressed in
terms of volume and entropy changes. The most important variables in our
treatment of thermodynamics are temperature (T), pressure (P), enthalpy
(H), entropy (S), internal energy (U), and volume (V). Some of these variables are extensive quantities (i.e., the property is proportional to the size
of the system. Examples of extensive variables include mass, volume,
energy, entropy, Gibbs energy (G), heat capacity (C), and number of moles
(n). All these depend on the amount of material present. In contrast,
intensive variables do not depend on the amount of material present.
Examples of intensive variables include density, concentration, temperature,
and molar heat capacity. Dividing an extensive property by a different
CHAPTER 2: Thermodynamics and Nanoscience
18
exchanges both energy and matter with its surroundings. However, if
transfer of energy but not matter is allowed, then we refer to the system as
being closed. The earth is an example of a (nearly) closed system, where
electromagnetic energy is exchanged between the earth and its surroundings but very little matter is exchanged. Actual systems are rarely
completely open or isolated, but can be approximated as such to simplify
the theoretical treatment of the system and distinguish systems with
greatly different degrees of heat or matter transfer. For example, coffee in
even a very well designed thermos (which can be approximated as an
isolated system) will eventually cool to room temperature, but it will
happen far slower than in a paper cup (open system).
Dynamic processes, such as a change in physical state or a chemical
reaction, can be described by the type of interaction that occurs between the
system and the surroundings. If such a process occurs with no heat transfer
between the system and surroundings, we call that process adiabatic.
An isothermal process is one where there is no change in temperature of
the system or the surroundings. A process occurring under conditions of
constant pressure is an isobaric process. Again, these are often ideal situations and, for example, an adiabatic process may in reality occur with a
slight transfer of heat to or from the surroundings, such as when a gas
cylinder becomes cold to the touch when vented rapidly. We use terminology such as open, closed, isolated, isothermal, adiabatic, and isobaric to
carefully define the state of a system and/or delineate the nature of the
process involving the interaction between the system and its surroundings.
2.1.2 Some thermodynamic variables
The thermodynamic state of a system is specified by a set of variables. For
example, the change in the internal energy of a system can be expressed in
terms of volume and entropy changes. The most important variables in our
treatment of thermodynamics are temperature (T), pressure (P), enthalpy
(H), entropy (S), internal energy (U), and volume (V). Some of these variables are extensive quantities (i.e., the property is proportional to the size
of the system. Examples of extensive variables include mass, volume,
energy, entropy, Gibbs energy (G), heat capacity (C), and number of moles
(n). All these depend on the amount of material present. In contrast,
intensive variables do not depend on the amount of material present.
Examples of intensive variables include density, concentration, temperature,
and molar heat capacity. Dividing an extensive property by a different
CHAPTER 2: Thermodynamics and Nanoscience
18