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The following are some definitions the student should know in order to understand the language of thermodynamics.
System: A defined physical space, whose boundaries usually correspond to some physical barrier or logical limit. Examples
Isolated System: A system which is entirely uninfluenced by changes outside the system. In particular, there is no possibility of the transfer of either energy or matter across the boundaries of the system. Detail
Closed System: A system in which there is the possibility of energy exchange with the environment, but there is no transfer of matter across the boundaries. This does not exclude the possibility of a change of internal composition due to chemical reaction. Detail
Open Systems: A system which can exchange both energy and matter with its environment. Detail
State Function A state function describes a physical property
of the system and is independent of how the system arrived at its present
condition. The state functions of interest are the physical quantities
associated with the system. Examples of state functions would be: pressure,
volume, temperature, number of particles or moles of material contained in
the system, the concentrations of matter contained in the system, etc. In
chemistry it is difficult to come up with properties that are not
state functions. Even some of these, for example a rate of reaction,
are determined largely by state functions.
| Type of System: | Ability to transfer energy between itself and the outside of the system | Ability to transfer matter between itself and the outside of the system |
| Isolated System | No transfer is possible | No transfer is possible |
| Closed System | Transfer is possible | No transfer is possible |
| Open System | Transfer is possible | Transfer is possible |
Surroundings: That portion of the universe which does not include the system in question. Thus, a universe consists of a system and its surroundings.
Spontaneous process: A process which requires no influence from outside the system to proceed. A process which can proceed in an isolated system.
Nonspontaneous process: A process which does require influence from outside the system to proceed. This process is impossible in an isolated system.
Equilibrium: A condition in which there is no net change in
any of the state functions of a system which has been allowed to arrive at
rest with its surroundings.
| For gases | 1 atm pressure* |
| For solutes (ions) | 1 M |
| For others | 1 mole fraction |