TOPIC 6

Question 1

What is Entropy?

Answer 1

The ENTROPY of a system can in fact be shown to be a measure of its disorder and of the UNAVAILABILITY OF ENERGY TO DO WORK.

Question 2

simple definition of energy

Answer 2

the ability to do work

Question 3

is a measure of how much energy is not available to do work.

Answer 3

entropy

Question 4

That unavailable energy is of interest in thermodynamics, because

Answer 4

the field of thermodynamics arose from efforts to convert heat to work.

Question 5

Unit of Entropy

Answer 5

J/K

KJ/K

Btu/°R

Question 6

Unit for Specific Entropy

Answer 6

KJ/kg K (for s)

KJ/kmol K (for s line)

Btu/lb °R (for s)

Btu/lbmol °R (for s line)

Question 7

Btu/°R to J/K

Answer 7

1899.1 J/K

Question 8

Btu to J

Answer 8

1055.06 J

Question 9

lb to kg

Answer 9

0.454 kg

Question 10

K to R

Answer 10

1.8 R

Question 11

Linear Interpolation Formula

Answer 11

y = y1 + x - x1 / x2 - x1 (y2 - y1)

Question 12

For saturation states, the values of sf and sg are tabulated as a function of

Answer 12

either saturation pressure or saturation temperature

Question 13

entropy of a two-phase liquid–vapor mixture is calculated using the quality

Answer 13

s = (1 - x) sf + xsg
= sf + x (sg - sf)

Question 14

the quality (x) of the mixture can be determined from the knows specific internal energy

Answer 14

x = u - uf / ug - uf

Question 15

Temperature–Entropy Diagram is also known as

Answer 15

T-s Diagram

Question 16

Enthalpy–Entropy Diagram is also known as

Answer 16

h-s diagram or Mollier diagram

Question 17

intended for evaluating properties at superheated vapor states and for two-phase liquid–vapor mixtures

Answer 17

h-s diagram or Mollier diagram

Question 18

is an expression of the second law that is particularly effective for thermodynamic analysis

Answer 18

entropy balance

Question 19

Entropy Balance for CLOSED Systems

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

(Equation) Entropy transfer

Answer 20

it is associated with heat transfer to or from the system during the process

Question 21

(Equation) Entropy transfer: it can be interpreted

Answer 21

entropy transfer accompanying heat transfer.

Question 22

(Equation) Entropy transfer

Answer 22

The direction of entropy transfer is the same as the direction of the heat transfer, and the same sign convention applies as for heat transfer:

Question 23

Positive value in entropy means

Answer 23

entropy is transferred into the system

Question 24

Negative value in entropy means

Answer 24

entropy is transferred out the system

Question 25

When there is NO HEAT TRANSFER

Answer 25

there is NO ENTROPY TRANSFER.

Question 25

The term σ is positive when

Answer 25

internal irreversibilities are present during the process and vanishes when no internal irreversibilities are present

Question 26

entropy is produced (or generated) within the system by

Answer 26

by the action of irreversibilities.

Question 27

Entropy production is a property?

Answer 27

Entropy production is not a property

Question 28

The second law requires that

Answer 28

entropy production be positive, or zero, in value:

Question 29

σ > 0

Answer 29

irreversibilities present within the system

Question 30

σ = 0

Answer 30

no irreversibilities present within the system

Question 31

The value of the entropy production (σ)

Answer 31

CANNOT BE NEGATIVE

Question 32

In contrast, the CHANGE IN ENTROPY (Δ S) of the system may be positive, negative, or zero:

Answer 32

. > 0 S2 - S1 = 0 < 0

Question 33

To evaluate the entropy transfer term of the entropy balance requires

Answer 33

information regarding both the heat transfer and the temperature on the boundary where the heat transfer occurs.