Name: ____________________________________________ Date: ______________ Section :_____________________
6.1, 6.2, 6.3 QUIZ: THERMODYNAMICS
Multiple Choice:
ANSWER: F
ANSWER: E
ANSWER: G
ANSWER: G
ANSWER: A
Multiple Selection:
Use the heating curve below, and identify which leg(s) of the curve fit the description.
_________A,C,E________ Kinetic energy is increasing
_________B________ Mixed solid and liquid
__________D_______ Evaporation
_________B,D________ Increasing potential energy
_____N/A – will go over in class Monday after exam_____ Phase with the greatest potential energy
________E_________ Phase with the greatest kinetic energy
________E_________ Phase with the greatest entropy
For the next blank, your answer should be a temperature.
_______100 C__________ The boiling point
For the next blanks, determine the Law of Thermodynamics (1st, 2nd, or 3rd) which best explains the phenomena described.
________2_________ When a teacher organizes her desk, the entropy of the desk decreases, but the entropy of the
universe still must increase.
_________2________ No engine can be 100% efficient.
________3_________ A crystal can never have zero kinetic energy, because its electrons must still be moving.
_______1__________ When a roller coaster speeds down a hill, its potential energy is transformed into kinetic energy
or is lost as heat through friction
Short Answer (Show all work. Box final answers with units):
1) The third law of thermodynamics states that a substance can never reach Absolute Zero. On a microscopic level,
explain why this is true.
All matter has kinetic energy—which on the macroscopic level we observe as temperature. A substance can
never reach absolute zero because, even at the coldest temperatures, the elementary particles in an atom will
still be moving, have energy, and therefore mass.
2) Why can an engine or motor never have an efficiency greater than 1? Explain your answer using the laws of
thermodynamics.
The keyword here is GREATER than one. An engine can never have a greater than one efficiency because more
work would have to be done than energy used or absorbed by the engine. As a result, the engine would have to
magically “create” energy, which is against the first law of thermodynamics since energy can never be created or
destroyed.
3) A system with an internal energy of 120 J has 81 J of heat added to it, and then the system does 56 J of work.
What is the final internal energy of the system?
ΔE = W + Q
Ef – Ei = W + Q
Ef – 120 = -56 + 81
Ef – 120 = 25
Ef = 145 J
4) A heat engine absorbs 5000 J of heat, then releases 1200 J of heat to a cold reservoir.
a. What is the work done by the heat engine?
For heat engines: ΔEcycle = 0
0 = Qabsorbed + W + Qreleased
0 = 5000 + W + -1200
W = -3800 J (- means work done by engine)
3800 J of work is done by the heat engine
b. What is the efficiency of the engine?
eff = W/Qabsorbed = 3800 / 5000 = 0.76
*remember Qabsorbed or W + Qreleased represents the total energy used during one cycle
5) A motor uses 600 J of energy to raise a 5 kg block to a height of 10 m. What is the efficiency of the motor?
eff = W/energy used
W = mgΔh = 5000(9.8)(10) = 490 J
Eff = 490/600 = 0.81