Examples of system in the following topics:

 A thermodynamic system can be any physical system with a welldefined volume in space.
 The outer edge of the system is referred to as its boundary, which often separates the system from the surroundings.
 Hence, q means the system loses heat, while +q means a system gains heat.
 Similarly, +w means work is done on the system, while w means work is done by the system.
 However, in open systems, the pressure of the system and the surroundings has stayed constant.

 For isolated systems, entropy never decreases.
 Increases in entropy correspond to irreversible changes in a system.
 This is because some energy is expended as heat, limiting the amount of work a system can do.
 The state function has the important property that in any process where the system gives up energy ΔE, and its entropy falls by ΔS, a quantity at least TR ΔS of that energy must be given up to the system's surroundings as unusable heat (TR is the temperature of the system's external surroundings).
 The entropy of a system is defined only if it is in thermodynamic equilibrium.

 Everything that is not a part of the system constitutes its surroundings.
 The system and surroundings are separated by a boundary.
 A closed system may still exchange energy with the surroundings unless the system is an isolated one, in which case neither matter nor energy can pass across the boundary.
 Conversely, heat flow out of the system or work done by the system (on the surroundings) will be at the expense of the internal energy, and q and w will therefore be negative.
 Isolated systems spontaneously evolve towards thermal equilibrium—the state of maximum entropy of the system.

 Energy can be shared between microstates of a system.
 With more available microstates, the entropy of a system increases.
 These processes reduce the state of order of the initial systems.
 With more available microstates, the entropy of a system increases.
 The more such microstates, the greater is the probability of the system being in the corresponding macrostate.

 The Gibbs free energy is the maximum amount of nonexpansion work that can be extracted from a closed system.
 Gibbs energy is the maximum useful work that a system can do on its surroundings when the process occurring within the system is reversible at constant temperature and pressure.
 The work is done at the expense of the system's internal energy.
 ΔG is the maximum amount of energy which can be "freed" from the system to perform useful work.
 "Useful" in this case, refers to the work not associated with the expansion of the system.

 The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches zero.
 At zero temperature the system must be in a state with the minimum thermal energy.
 A more general form of the third law applies to systems such as glasses that may have more than one minimum energy state: the entropy of a system approaches a constant value as the temperature approaches zero.
 The constant value (not necessarily zero) is called the residual entropy of the system.
 For such systems, the entropy at zero temperature is at least ln(2)kB, which is negligible on a macroscopic scale.

 Gibbs free energy measures the useful work obtainable from a thermodynamic system at a constant temperature and pressure.
 The Gibbs free energy is the maximum amount of nonexpansion work that can be extracted from a closed system.
 When a system changes from an initial state to a final state, the Gibbs free energy (ΔG) equals the work exchanged by the system with its surroundings, minus the work of the pressure force.
 Gibbs energy (also referred to as ∆G) is also the chemical potential that is minimized when a system reaches equilibrium at constant pressure and temperature.

 The International System of Units (abbreviated SI) is the metric system used in science, industry, and medicine.
 The International System of Units (abbreviated SI, from the French Système international d'unités) is the metric system used in science, industry, and medicine.
 The imperial system is used for "everyday" measurements in a few places, such as the United States.
 The use of the SI system provides all scientists and engineers with a common language of measurement.
 Causey teaches scientific units of the SI system, the metric system, and the CGS system.

 In thermodynamics, work (W) is defined as the process of an energy transfer from one system to another.
 The first law of thermodynamics states that the energy of a closed system is equal to the amount of heat supplied to the system minus the amount of work done by the system on its surroundings.
 The amount of energy for a closed system is written as follows:
 In this equation, U is the total energy of the system, Q is heat, and W is work.
 By adding the PV term, it becomes possible to measure a change in energy within a chemical system, even when that system does work on its surroundings.

 The following examples refer to a two component system, in which one monomer is designated A and the other B.