chapter 4 🤑🤑🤑🤑 Flashcards
Boltzmann Definition of Entropy (don’t use)
S_=klnW
S_=entropy
k= boltzmann’s constant
W= ways of arranging molecules
simple system
not acted on by external forces or inertial forces; no internal temperature gradients or composition gradients; no internal rigid, adiabatic, or impermeable walls
Macroscopic Definition of Entropy
SECOND LAW OF THERMO
intensive entropy is a property of the system. for a differential change of state of a closed simple system, the differential entropy change of the system is equal to the heat absorbed by the system along a reversible path divided by the absolute temperature of the system at the surface where heat is transferred.
What does entropy change with?
volume (pressure) and temperature
Explain Entropy of the Universe
entropy may decrease in one part of a system but must increase in another part. Entropy is connected with maximum process efficiency
3 parts of framework/principle of second law
1) irreversible processes will result in an increase in entropy of the universe, (irreversible processes result in entropy generation. irreversible process results in loss of capability for performing work)
2) reversible process result in no increase in entropy of the universe. (reversible processes result in zero entropy generation. this principle will be useful for calculation of maximum work output or minimum work input for a process)
3) proposed processes which would result in a decrease of entropy of the universe are impossible. (impossible processes result in negative entropy generation).
SECOND LAW OF THERMO (THE ENTROPY BALANCE)
reversible processes and/or optimum work interaction occur without entropy generation and irreversible processes result in entropy generation. (entropy of the universe is always increasing)
Is entropy a state property?
entropy is a state property. for a single phase fluid, specific entropy is characterized by two state variable (T,P,etc.)
Isentropic
constant entropy deltaS=o
When is a process irreversible?
When the entropy change for the universe is positive.
internally reversible
a process that is irreversible due to interactions at the boundaries even when each system in the process is reversible.
no entropy generation INSIDE the system boundaries, work not lost inside device
Are throttles reversible or irreversible?
throttles are always irreversible
processes that generate entropy
1) heat conduction along a temperature gradient
2) diffusion along a concentration gradient
3) mixing of substances of different composition
4) adiabatic mixing at constant system volume of identical substances initially at different molar entropy due to differences in T&P
5) Velocity gradients within equipment
6) friction
7) electrical resistance
8) chemical reactions at measurable rates
does a reversibility assumption over or under estimate work
over (according to hw i actually have no idea)
throttles are…..
isenthalpic and isothermal
