Topic 5

Question 1

The most fundamental law of
science

Answer 1

Second Law of Thermodynamics

Question 2

Charles Percy Snow in his Two Cultures wrote

Answer 2

“Not knowing the Second Law of Thermodynamics is like never having read a work of Shakespeare”

Question 3

CBE was a novelist and English physical chemist who also served in several important positions in the British Civil Service and briefly in the UK government.

Answer 3

Charles Percy Snow, Baron Snow

Question 4

How highly Einstein regarded thermodynamics can be appreciated in the following quote

Answer 4

“A law is more impressive the greater the simplicity of its premises, the more different are the kinds of things it relates, and the more extended its range of applicability. It is the only physical theory of universal content, which I am convinced, that within the framework of applicability of its basic concepts will never be overthrown”

Question 5

The second law of Thermodynamics simply means

Answer 5

“How things work, and why things work”

Question 6

In fact in modern times the second law of
thermodynamics is

Answer 6

second law of thermodynamics is being used to even explain popular theories like big bang, expansion of the cosmos and how the time is fast tickling away towards the “heat death” of the universe

Question 7

Aspects of the Second Law

Answer 7

1. Predicting the direction of processes
2. Establishing conditions for equilibrium
3. Determining the best theoretical performance of cycles, engines, and other devices.
4. Evaluating the quantitatively the factors that preclude the attainment of the best theoretical performance.
5. Defining a temperature scale
6. Developing means for evaluating properties

Question 8

Three alternative statements of the second law of thermodynamics:

Answer 8

Traditional formulations of the second law
1. Clausius statement
2. Kelvin-Planck statement
3. Entropy statement

Question 9

The Clausius statement of the second law asserts that:

Answer 9

“It is impossible for any system to operate in such a way that the sole result would be an energy transfer by heat from a cooler to a hotter body”

Question 10

• contributed to the theory of electrolysis (the
  breaking down of a compound by electricity)

GERMAN MATHEMATICIAN AND PHYSICIST

one of Europe’s elite theoretical physicists, was born in Köslin, Poland, in 1822.

Answer 10

Rudolf Julius Emanuel Clausius

Question 11

Kelvin-Planck statement of the second law

Answer 11

“It is impossible for any system to operate in a thermodynamic cycle and deliver a net amount of energy by work to its surroundings while receiving energy by heat transfer from a single thermal reservoir”

Question 12

a special kind of system that always remains at constant temperature even though energy is added or removed by heat transfer.

Answer 12

Thermal reservoir / reservoir

Question 13

sequence of processes that begins and ends at the same state.

Answer 13

Thermodynamic cycle

Question 14

Analytical form of the Kelvin–Planck statement

Answer 14

W(cycle) ≤ 0 (single reservoir)

Question 15

• Devising the absolute
  temperature scale, now called
  the ‘Kelvin scale’
• Formulating the second law of
  thermodynamics
• Working to install telegraph
  cables under the Atlantic.

Answer 15

Lord Kelvin

Question 16

He was able to deduce the relationship between the energy and the frequency of radiation.

Answer 16

Max Karl Ernst Ludwig Planck

Question 17

the equivalence of the Clausius and Kelvin – Planck statements of the second law

Answer 17

W(cycle) = Q(H) - Q(C)

Question 18

Entropy Statement of the Second Law

Answer 18

 Mass and energy are familiar examples of extensive properties of systems.

 Entropy is another important extensive property.

 Entropy balance

Question 19

Entropy Balance

Answer 19

(change in the amount of entropy contained within the system during some time interval)
=
(net amount of entropy transferred in across the system boundary during the time interval)
+
(amount of entropy produced within the system during the time interval)

Question 20

Unlike mass and energy, which are conserved

Answer 20

entropy is produced (or generated) within systems whenever nonidealities (called irreversibilities) such as friction are present.

Question 21

Entropy statement of the second law

Answer 21

“It is impossible for any system to operate in a way that entropy is destroyed”

Question 22

a process that can be reversed without
leaving any trace on the surroundings. It means both system and surroundings are returned to their initial states at the end of the reverse process.

do not occur

idealizations of actual processes.

things happen very slowly, without any resisting force, without any space limitation

everything happens in a highly organized way

Answer 22

Reversible process

Question 23

one in which heat is transferred through a finite temperature.

Answer 23

Irreversible process

Question 24

if no irreversibilities occur within the boundaries of the system

system undergoes through a series of equilibrium states, and when the process is reversed, the system passes through exactly the same equilibrium states while returning to its initial state.

Answer 24

Internally reversible process:

Question 25

if no irreversibilities occur outside the system
boundaries during the process.

Heat transfer between a reservoir and a system is an externally reversible process if the surface of contact between the system and reservoir is at the same temperature.

Answer 25

Externally reversible process:

Question 26

Totally reversible (reversible):

Answer 26

both externally and internally reversible processes.

Question 27

Two types of Irreversabilities

Answer 27

External irreversibilities
Internal irreversibilities

Question 28

These are associated with dissipating effects outside the working fluid.

ex. Mechanical friction occurring during a
process due to some external source.

Answer 28

External irreversibilities

Question 29

These are associated with dissipating effects within the working fluid.

ex. Unrestricted expansion of gas, viscosity and
inertia of the gas.

Answer 29

Internal irreversibilities

Question 30

Commonly encountered causes of irreversibilities

Answer 30

Friction
Mixing of two fluids
electric resistance

Question 31

Thermal Efficiency of the cycle is

Answer 31

n = W(cycle) / Q(H) = 1 - Q(C) / Q(H)

Question 32

refrigeration cycle the coefficient of performance (COP) is

Answer 32

β = Q(C) / W(cycle) = Q(C) / Q(H) - Q(C)

Question 33

The coefficient of performance (COP) for a
heat pump cycle is

Answer 33

γ = Q(H) / W(cycle) = Q(H) / Q(H) - Q(C)

Question 34

Corollaries of the Second Law for Refrigeration and Heat Pump Cycles

Answer 34

1. The coefficient of performance of an irreversible refrigeration cycle is always less than the coefficient of performance of a reversible refrigeration cycle when each operates between the same two thermal reservoirs.
2. All reversible refrigeration cycles operating between the same two thermal reservoirs have the same coefficient of performance.

Note: By replacing the term refrigeration with heat pump, we obtain counterpart corollaries for heat pump cycles.

Question 35

Carnot Efficiency

Answer 35

n(max) = 1 - T(C) / T(H)

The value of the Carnot efficiency increases as 𝑻𝑯 increases and/or 𝑻𝑪 decreases.

Question 36

Thermal efficiency of a system undergoing a
reversible power cycle while operating between
thermal reservoirs at temperatures 𝑇𝐻 and 𝑇𝐶 .

Answer 36

Carnot Efficiency

Question 37

Coefficient of performance of any system undergoing a reversible refrigeration cycle while operating between the two reservoirs:

Answer 37

β(max) = T(C) / T(H) - T(C)

Question 38

Coefficient of performance of any system undergoing a reversible heat pump cycle while operating between the two reservoirs:

Answer 38

γ(max) = T(H) / T(H) - T(C)

Question 39

n < n(max)

Answer 39

cycle operates Irrevesibly

Question 40

n > n(max)

Answer 40

the power cycle is impossible

Question 41

n = n(max)

Answer 41

the cycle operates reversibly

Question 42

the temperatures used to evaluate βmax and γmax

Answer 42

It must be absolute temperatures on the Kelvin or Rankine scale.

Question 43

the system executing the cycle undergoes a series of four internally reversible processes

Answer 43

Carnot Cycle

Question 44

two adiabatic processes

alternated with two isothermal processes.

an ideal reversible closed thermodynamic cycle

Answer 44

Carnot cycle

Question 45

The four processes of the cycle are:

Answer 45

Process 1–2:
The gas is compressed adiabatically to state 2, where the temperature is T(H)

Process 2–3:
The assembly is placed in contact with the reservoir at T(H). The gas expands isothermally while receiving energy Q(H) from the hot reservoir by heat transfer.

Process 3–4:
The assembly is again placed on the insulating stand and the gas is allowed to continue to expand adiabatically until the temperature drops to T(C)

Process 4–1:
The assembly is placed in contact with the reservoir at TC. The gas is compressed isothermally to its initial state while it discharges energy QC to the cold reservoir by heat transfer.

Question 46

Second law of Thermodynamics states that

Answer 46

The Second Law of Thermodynamics states that in any natural process, the total entropy of an isolated system always increases or remains constant but never decreases.