Week 4 Lecture 6

Question 1

imposes restrictions on the direction of actual processes

Answer 1

second law of thermodynamics

Question 2

Statements of the second law

Answer 2

• No apparatus can operate in such a way that it only effect is to convert heat absorbed by a system. It is impossible by a cyclic process to convert the heat absorbed by a system completely into work done by the system
• No process is possible which consists sole in the transfer of heat from one temperature level to a higher one

Question 3

device that takes in energy by heat and operating in a cyclic process, expels a fraction of that energy by means of work

Answer 3

heat engine

Question 4

A heat engine carries some working substance through a ____ process

Answer 4

cyclical

Question 5

heat engine steps

Answer 5

1. Working substance absorbs energy by heat from a higher temperature reservoir
2. Work is done by the engine (Weng)
3. Energy is expelled as heat to lower temperature reservoir (Qc)

Question 6

First law equation
Qh =

Answer 6

Qh = Weng + Qc

Question 7

efficiency equation
η =

Answer 7

net work output/heat input

Question 8

efficiency equation
η =

Answer 8

|W eng|/|Qh|

Question 9

efficiency equation
η =

Answer 9

|Qh|- |Qc|/|Qh|

Question 10

efficiency equation
η =

Answer 10

1- (|Qc|/|Qh|)

Question 11

High value of η meanings good conversion of …

Answer 11

Qh to Weng

Qc = 0

Question 12

heat engine in inverse steps

Answer 12

1. Energy is extracted from the cold reservoir (Qc) by work done on the heat pump (W)
2. Energy is transferred to the hot reservoir (Qh)
3. This process means the heat engine is running as a heat pump

Question 13

Measured the performance of the heat pump running in cooling mode

Answer 13

Coefficient of performance (COP)

Question 14

COP equation for cooling mode

Answer 14

|Qc|/W

Question 15

COP equation for heating mode

Answer 15

|Qh|/W

Question 16

depends only on the temperature between which it operates and is independent of the nature of the cyclic process

Answer 16

maximum efficiency

Question 17

|Qh|/|Qc|=

Answer 17

Th / Tc

Question 18

1 - Tc/Th =

Answer 18

η

Question 19

|Qh|/ Th =|Qc|/ Tc

Answer 19

Reversible heat engine

Question 20

|Qh|/ Th <|Qc|/ Tc

Answer 20

Irreversible heat engine

Question 21

|Qh|/ Th >|Qc|/ Tc

Answer 21

Impossible heat engine

Question 22

Entropy ____ with temperature

Answer 22

increases

Question 23

amount or degree of disorder or randomness of a system

Answer 23

Entropy

Question 24

If a system moves from a state of non equilibrium toward equilibrium, entropy is ____

Answer 24

created

Question 25

Systems will spontaneously move from non equilibrium states to ________ but NOT VICE VERSA

Answer 25

equilibrium states

Question 26

System will only spontaneously move toward states that ________ the total entropy in the universe

Answer 26

maximise

Question 27

2nd Law of Thermodynamics

Answer 27

Entropy can be created by never destroyed

This makes entropy fundamentally different from energy and mass, which must always be conserved

Question 28

A system undergoing a ____ process is always at equilibrium, and therefore does not create entropy

Answer 28

reversible

Question 29

A system undergoing a reversible process is always at ____, and therefore does not create entropy

Answer 29

equilibrium

Question 30

A system undergoing a reversible process is always at equilibrium, and therefore does not create ______

Answer 30

entropy

Question 31

All ____ processes are driven by a system moving from a non-equilibrium state toward equilibrium and therefore all real processes create entropy and are irreversible

Answer 31

real

Question 32

All real processes are driven by a system moving from a________ state toward equilibrium and therefore all real processes create entropy and are irreversible

Answer 32

non-equilibrium

Question 33

All real processes are driven by a system moving from a non-equilibrium state toward equilibrium and therefore all real processes create ____ and are irreversible

Answer 33

entropy

Question 34

All real processes are driven by a system moving from a non-equilibrium state toward equilibrium and therefore all real processes create entropy and are ______

Answer 34

irreversible

Question 35

The entropy of the Universe should ultimately reach a maximum. At this time the universe will be at a state of uniform temperature and density. This state of perfect disorder implies no energy will be available for doing work.

Answer 35

Heat death of the universe

Question 36

When energy is ____, Q is positive and entropy increases

Answer 36

absorbed

Question 37

When energy is absorbed, Q is ____ and entropy increases

Answer 37

positive

Question 38

When energy is absorbed, Q is positive and entropy ____

Answer 38

increases

Question 39

When energy is ____, Q is negative and entropy decreases

Answer 39

expelled

Question 40

When energy is expelled, Q is ____ and entropy decreases

Answer 40

negative

Question 41

When energy is expelled, Q is negative and entropy _____

Answer 41

decreases