The second law

Question 1

What is the second law?

Answer 1

Heat will always flow spontaneously from hot regions to cold regions
This is a macroscopic and empirical law

Question 2

What is the work done by an engine?

Answer 2

W=Qh+Qc
Where Qh=+
Qc=-

Question 3

What is the efficiency of an engine?

Answer 3

ε =W/Qh=1-abs(Qc/Qh)

Question 4

What is the performance coefficient of a fridge?

Answer 4

K=abs(Qc/W)=abs(Qc/(Qh-abs(Qc))

Question 5

What is the performance coefficient of a heat pump?

Answer 5

K=abs(Qh/W)

Question 6

What is the Carnot cycle?

Answer 6

A theoretical concept of the most efficient cycle for a heat engine

Question 7

How does the Carnot cycle work?

Answer 7

Isotherm at Th
Adiabat
Isotherm at Tc
Adiabat

Question 8

What is the work done for a Carnot cycle?

Answer 8

W=Q=nR(Th-Tc)ln(V2/V1)

Question 9

What is the efficiency of the Carnot cycle?

Answer 9

ε = 1 −Tc/Th
T must always be in Kelvin

Question 9

What is the most efficient cycle?

Answer 9

A reversible cycle

Question 9

Are all real processes reversible or irreversible?

Answer 9

Irreversible

Question 9

What is entropy?

Answer 9

A measure of how random a system has become

Question 10

How is entropy determined?

Answer 10

Entropy is a function of state

Question 11

What is the equation for entropy?

Answer 11

dS=dQ/T
∆S=Q/T

Question 12

What is ∆S for a reversible process?

Answer 12

∆S=nRln(V2/V1)

Question 13

How is ∆S found for an irreversible process?

Answer 13

By finding a combination of reversible processes for which ∆S=Q/T can be used

Question 14

What is ∆S for an adiabatic process?

Answer 14

∆S=0