Entropy Flashcards
(25 cards)
What does the Clausius Equality state for a reversible cycle?
∮ dQrev / T =0
What does entropy change depend on?
Only on the initial and final states (state function), not the path.
What is the differential form of entropy change?
dS= dQ rev / T
What does the First Law become in terms of entropy?
dU=TdS−PdV
For a reversible process with constant heat capacity, what is Δ𝑆?
Δ𝑆 = 𝐶𝑃*ln(𝑇𝑓/𝑇𝑖)
When does entropy increase in a system?
When heat flows into the system (i.e. 𝑇𝑓 > 𝑇𝑖)
When does entropy decrease?
When heat flows out (i.e. 𝑇𝑓 < 𝑇𝑖)
When does entropy decrease?
When heat flows out (i.e. 𝑇𝑓 < 𝑇𝑖)
What happens to Δ𝑆 if 𝑇𝑓 = 𝑇𝑖?
ΔS=0
How do you calculate entropy change for a solid with variable 𝐶𝑉(𝑇)?
ΔS=∫ CV(T) / T dT
What does the Clausius Inequality state for an irreversible cycle?
∮ 𝑑𝑄/𝑇 < 0
What does this imply about entropy?
dS ≥ dQ/T
What is the entropy change in an isolated system during an irreversible process?
It must increase: Δ𝑆 > 0
What is the second law of thermodynamics (entropy form)?
In any irreversible process, the total entropy of the system increases.
What is the entropy change of the thermodynamic universe?
ΔS univ = ΔS system + ∑ΔS reservoirs
What happens to Δ𝑆univ in a reversible process?
ΔS univ = 0
What happens to Δ𝑆 univ in an irreversible process?
ΔS univ > 0
What does entropy tell us about time?
It gives the “arrow of time”—entropy increases as time progresses.
What is the entropy change of a standard Carnot engine cycle?
ΔS univ = 0
In a modified Carnot engine with irreversible heat flow, what happens to entropy?
Entropy increases in the auxiliary reservoir.
What is the entropy change due to irreversible heat flow?
ΔS=Q1(1/ T1* − 1/T1)
What is the lost work due to irreversible heat flow?
ΔW=T2*ΔSmodified
What is the Helmholtz free energy?
F=U−TS
What does the Helmholtz free energy represent?
The amount of energy available to do useful work.
