Chapter 7: Entropy Flashcards
what is the Clausius inequality?
the cyclic integral of 1/T dQ is always less than or equal to zero
for totally or internally reversible cycles = 0
for irreversibly cycles < 0
what kind of property is entropy?
state property
the entropy change between 2 specified states is the same whether the process is reversible or irreversible
what is entropy?
measure of disorder/randomness
change in heat transfer over temperature
what is entropy in an internally reversible isothermal process?
heat transfer over constant temperature
what is entropy in reversible adiabatic process?
S = 0, no heat transfer
constant entropy, also known as isentropic process
when is entropy generated?
during an irreversible process due to the presence of irreversibilities
always positive quantity or zero (if reversible process)
what is the entropy in a isolated closed system?
heat transfer in isolated system is zero
if irreversible process, entropy increases
if reversible process, entropy constant
what is total entropy change in isolated system?
sum of entropy changes of system and its surroundings (equal to entropy generated)
can entropy change be negative?
yes, it can due to heat loss for example
however, entropy generation cannot
what is the direction of process?
direction of increase of entropy
process that violates this principle is impossible
is entropy a conserved property?
no, it increases during all actual processes
it is only conserved during idealized reversible processes
what does area under temperature-entropy (T-S) diagram represent?
heat transfer for internally reversible processes
what are the 2 relations between temperature and change in entropy?
1) Gibbs equation
TdS = dU + PdV
2) TdS = DH - VdP
2 relationships are valid both both reversible/irreversible processes and closed/open systems
what is the temperature and change in entropy relationship for incompressible substances (i.e., solid & liquids)?
TdS = dU = cdT, where c is specific heat (c = cp = cv)
what is relationship between temperature of incompressible substance and entropy during an isentropic process?
temp remains constant during isentropic process
Therefore, isentropic process is also isothermal
