Worksheet #30: Entropy - Iowa State University

Worksheet #30: Entropy
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Brian
PHYS 221
Ho
5/01/2014
1. Two 2.00 kg copper slabs are initially at 0.00 C and 80.0 C, respectively. They are then
placed in thermal contact, so soon they are both at 40.0 C. Assume that the system is
thermally insulated, so heat flows between the slabs. What is the change in entropy of
this system?
A.
B.
C.
D.
E.
-98.3 J/K
0 J/K
12.8 J/K
107 J/K
200 J/K
2. A hot piece of iron is thrown into the ocean and its temperature eventually stabilizes.
Which of the following statements about the process is correct?
A.
B.
C.
D.
E.
The entropy lost by the iron is equal to the entropy gained by the ocean.
The ocean gains more entropy than the iron loses.
The entropy gained by the iron is equal to the entropy lost by the ocean.
The change in the entropy of the iron-ocean system is zero.
The ocean gains less entropy than the iron loses.
3. Find the change in entropy for an ideal gas that undergoes isothermal expansion from an
initial volume to a final volume that is 200% of the initial volume.
A.
B.
C.
D.
E.
n*R*ln(2)
(R/2*ln(1/2))*n
(R/4)/n
½*ln(4)*n
ln(4)*(n/2)
4. A heat reservoir at 50 C is used to melt 25.0 kg of ice at 0 C. What is the entropy change
in the ice? What is the entropy change in the reservoir? (Lf for water = 3.35 X 10^5 J/K)
A.
B.
C.
D.
E.
26,600 J/K, 33,000 J/K
25,400 J/K, 16,600 J/K
-26,600 J/K, 26,000 J/K
26,600 J/K, -26,600 J/K
30,700 J/K, 25,900 J/K
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