Glossary
to accompany
Thermodynamics: An Engineering Approach, 5th edition
by Yunus A. Çengel and Michael A. Boles16Entropy balance relation for a control volume states that the rate of entropy change
within the control volume during a process is equal to the sum of the rate of entropy
transfer through the control volume boundary by heat transfer, the net rate of entropy
transfer into the control volume by mass flow, and the rate of entropy generation within
the boundaries of the control volume as a result of irreversibilities.
Entropy balance relation in general is stated as the entropy change of a system during a
process is equal to the net entropy transfer through the system boundary and the entropy
generated within the system as a result of irreversibilities.
Entropy change of a closed system is due to the entropy transfer accompanying heat
transfer and the entropy generation within the system boundaries and is greater than or
equal to the integral over the process of δQ/T.
Entropy departure is the difference between the entropy of a real gas at a given P and T
and the entropy of the gas at an ideal gas state at the same P and T.
Entropy departure factor is the nondimensionalized form of the entropy departure.
Entropy generation Sgen is entropy generated or created during an irreversible process, is
due entirely to the presence of irreversibilities, and is a measure of the magnitudes of the
irreversibilities present during that process. Entropy generation is always a positive
quantity or zero. Its value depends on the process, and thus it is not a property.
Entropy transfer is the transfer of entropy across a boundary by heat or mass.
Environment refers to the region beyond the immediate surroundings whose properties
are not affected by the process at any point.
Equation of state is any equation that relates the pressure, temperature, and specific
volume of a substance. Property relations that involve other properties of a substance at
equilibrium states are also referred to as equations of state.
Equilibrium implies a state of balance. In an equilibrium state there are no unbalanced
potentials (or driving forces) within the system. A system in equilibrium experiences no
changes when it is isolated from its surroundings.
Equilibrium constant for an equilibrium reaction is the ratio of the product of the
product component’s partial pressure raised to their stoichiometric coefficients and the
product of the reactant component’s partial pressure raised to their stoichiometric
coefficients. The equilibrium constant of an ideal-gas mixture at a specified temperature
can be determined from knowledge of the standard-state Gibbs function change at the
same temperature. The number of equilibrium constant relations needed to determine the