Thermodynamics and Propulsion | |

## 5.6 Muddiest Points on Chapter 5
MP 5..1
Why is
always true?
MP 5..2
What makes
different than
?
MP 5..3
What happens when all the energy in the universe is
uniformly spread, i.e., entropy at a maximum?
MP 5..4
Why do you rewrite the entropy change in terms of
?
MP 5..5
What is the difference between isentropic and adiabatic?
MP 5..6
In the single reservoir example, why can the entropy
decrease?
MP 5..7
Why does the entropy of a heat reservoir change if the
temperature stays the same?
Substituting for the atmospheric mass and the specific heat gives a
value for temperature change of roughly
K. To a very good
approximation, we can say that the temperature of this heat
reservoir is constant and we can evaluate the entropy change of the
reservoir as
.
MP 5..8
How can the heat transfer from or to a heat reservoir be
reversible?
MP 5..9
How can
be less than zero in any process? Doesn't
entropy always increase?
MP 5..10
If
for a reservoir, could you add
to any
size reservoir and still get the same
?
MP 5..11
What is the difference between the isothermal expansion of a
piston and the (forbidden) production of work using a single
reservoir?
- The reservoir loses heat .
- The system does work (equal in magnitude to ).
- The system changes its volume and pressure.
- The system changes its entropy (the entropy increases by ).
- The reservoir loses heat .
- The system does work ( ) and that's all the changes that there are. I leave it to you to calculate the total entropy changes (system plus surroundings) that occur in the two processes.
MP 5..12
For the ``work from a single heat reservoir'' example, how
do we know there is no
?
MP 5..13
How does a cycle produce zero
? I thought that the
whole thing about cycles was an entropy that the designers try to
minimize.
MP 5..14
On the example of free expansion versus isothermal
expansion, how do we know that the pressure and volume ratios are
the same? We know for each that
and
.
MP 5..15
Where did
come from?
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