Q1) A certain heat engine draws 500 J/s from a water bath at
27oC and rejects 400 J/s to a reservoir at a lower
temperature. The efficiency of this engine is:
1) 80%
2) 75%
3) 55%
4) 25%
5) 20%
Q2) The maximum theoretical efficiency of a Carnot heat
engine operating between reservoirs at the steam point and at
room temperature is about:
1) 10%
2) 20%
3) 50%
4) 80%
5) 99%
Q3) A Carnot heat engine runs between a cold reservoir at
300 K and a hot reservoir at 400 K. Which of the following
changes results in the greatest increase in its efficiency?
1) raise the temperature of the hot reservoir by 50 K
2) raise the temperature of the cold reservoir by 50 K
3) lower the temperature of the hot reservoir by 50 K
4) lower the temperature of the hot reservoir by 50 K
Q4) A Carnot heat engine and an irreversible heat engine both
operate between the same high temperature and low temperature
reservoirs. They absorb the same energy from the high temperature
reservoir as heat. The irreversible engine:
1) does more work
2) transfers more energy to the low temperature reservoir as heat
3) has the greater efficiency
4) has the same efficiency as the reversible engine
5) cannot absorb the same energy from the high temperature
reservoir as heat without violating the second law of thermodynamics
Q5) A Carnot refrigerator runs between a cold reservoir at
300 K and a hot reservoir at 400 K. Which of the following
changes results in the greatest increase in its coefficient of
performance?
1) raise the temperature of the hot reservoir by 50 K
2) raise the temperature of the cold reservoir by 50 K
3) lower the temperature of the hot reservoir by 50 K
4) lower the temperature of the hot reservoir by 50 K
Q6) Is it possible to cool down a well insulated room on
a hot summer day by leaving the refrigerator door
open?
1) yes
2) no
Q7) In a thermally insulated kitchen, an ordinary refrigerator is
turned on and its door is left open. The temperature of the room:
1) remains constant according to the first law of thermodynamics
2) increases according to the first law of thermodynamics
3) decreases according to the first law of thermodynamics
4) remains constant according to the second law of thermodynamics
5) increases according to the second law of thermodynamics
Q8) The difference in entropy S = SB - SA for two states A and B
of a system can be computed as the integral  ∫ dQ/T provided:
1) A and B are on the same adiabat
2) A and B have the same temperature
3) a reversible path is used for the integral
4) the change in internal energy is first computed
5) the energy absorbed as heat by the system is first computed
Q9) You finally decided to clean your room and pick up all the
clothes scattered on the floor and place them folded neatly in a
drawer. Has the entropy of the universe increased, decreased, or
stayed the same?
1) increased
2) decreased
3) stayed the same
Q10) Rank the entropy changes of the water as its temperature
rises
(a) from 20°C to 30°C,
(b) from 30°C to 35°C, and
(c) from 80°C to 85°C,
greatest first.
1) a, b, c
4) b = c, a
2) a, b = c
5) none of the above
3) c, b, a
Q11) Rank, from smallest to largest, the changes in entropy of a
pan of water on a hot plate, as the temperature of the water
1. goes from 20º C to 30º C
2. goes from 30º C to 40º C
3. goes from 40º C to 45º C
4. goes from 80º C to 85º C
1) 1, 2, 3, 4
2) 4, 3, 2, 1
3) 1 and 2 tie, then 3 and 4 tie
4) 3 and 4 tie, then 1 and 2 tie
5) 4, 3, 2, 1
Q12) A gas, confined to an insulated cylinder, is compressed
adiabatically (and reversibly) to half its original volume. Does the
entropy of the gas increase, decrease, or remain unchanged during
this process?
1) increase
2) decrease
3) remain unchanged
Q13) Consider all possible isothermal contractions of an ideal gas.
The change in entropy of the gas:
1) is zero for all of them
2) does not decrease for any of them
3) does not increase for any of them
4) increases for all of them
5) decreases for all of them
Q14) Consider the following processes: The temperature of two identical
gases are increased from the same initial temperature to the same final
temperature. Reversible processes are used. For gas A the process is
carried out at constant volume while for gas B it is carried out at constant
pressure. The change in entropy:
1) is the same for A and B
2) is greater for A
3) is greater for B
4) is greater for A only if the initial temperature is low
5) is greater for A only if the initial temperature is high
Q15) An ideal gas has temperature T1 at the initial state i shown in
the p-V diagram here. The gas has a higher temperature T2 at final
states a and b, which it can reach along the paths shown. Is the
entropy change along the path to state a larger than, smaller than,
or the same as that along the path to state b?
1) greater than
2) smaller than
3) the same as
Q16) An ideal gas is taken reversibly from state i, at temperature
T1, to another state, at temperature T2. Of the five processes shown
on the p-V diagram below, which results in the greatest change in
the entropy of the gas?
1) A
2) B
3) C
4) D
5) E
Q17) The change in entropy is zero for:
1) reversible adiabatic processes
2) reversible isothermal processes
3) reversible processes during which no work is done
4) reversible isobaric processes
5) all adiabatic processes
Q18) A hot object and a cold object are placed in thermal contact and the
combination is isolated. They transfer energy until they reach a common
temperature. The change Sh in the entropy of the hot object, the change
Sc in the entropy of the cold object, and the change Stotal in the entropy
of the combination are:
1) Sh > 0, Sc > 0, Stotal > 0
2) Sh < 0, Sc > 0, Stotal > 0
3) Sh < 0, Sc > 0, Stotal < 0
4) Sh > 0, Sc < 0, Stotal > 0
5) Sh > 0, Sc < 0, Stotal < 0
Q19) Let SI denote the change in entropy of a sample for an
irreversible process from state A to state B. Let SR denote the
change in entropy of the same sample for a reversible process from
state A to state B. Then
1) SI > SR
2) SI = SR
3) SI < SR
4) SI = 0
5) SR = 0
Q20) For all reversible processes involving a system and its
environment:
1) the entropy of the system does not change
2) the entropy of the system increases
3) the total entropy of the system and its environment does not
change
4) the total entropy of the system and its environment increases
5) none of the above
Q21) For all irreversible processes involving a system and its
environment:
1) the entropy of the system does not change
2) the entropy of the system increases
3) the total entropy of the system and its environment does not
change
4) the total entropy of the system and its environment increases
5) none of the above
Q22) If the configuration of molecules in a gas at temperature T
changes isothermally and reversibly so the multiplicity is increased
to three times its previous value the heat input to the gas is
1) Q = 0
2) Q = 3kT
3) Q = -3kT
4) Q = kT ln3
5) Q = -kT ln3
Q23) Three Carnot engines operate between reservoir temperatures of
(a) 400 and 500 K,
(b) 600 and 800 K,
and
(c) 400 and 600 K.
Rank the engines according to their thermal efficiencies, greatest first.
1) a, b, c
4) b = c, a
2) a, b = c
3) c, b, a
5) none of the above
Q24) You wish to increase the coefficient of performance of an ideal
refrigerator. You can do so by
(a) running the cold chamber at a slightly higher
temperature,
(b) running the cold chamber at a slightly lower
temperature,
(c) moving the unit to a slightly warmer room, or
(d) moving it to a slightly cooler room.
The magnitudes of the temperature changes are to be the same in all four
cases. Which of the changes result in the largest coefficients of
performance. Which result in the smallest.
1) largest: b; smallest a
4) largest: a; smallest b
2) largest: c; smallest d
5) none of the above
3) largest: a; smallest c
Q25) A box contains one mole of a gas. Consider two
configurations:
(a) each half of the box contains half the molecules, and
(b) each third of the box contains one-third of the
molecules.
Which configuration has more microstates?
1) a
2) b
3) not enough information
Q26) The temperature of n moles of a gas is increased from Ti to Tf
at constant volume. If the molar specific heat at constant volume is
CV and is independent of temperature, then change in the entropy
of the gas is:
1) nCV ln(Tf/Ti)
2) nCV ln(Ti/Tf )
3) nCV ln(Tf - Ti)
4) nCV ln(1 - Ti/Tf )
5) nCV (Tf - Ti)
Q27) An ideal gas, consisting of n moles, undergoes a reversible
isothermal process during which the volume changes from Vi to Vf.
The change in entropy of the thermal reservoir in contact with
the gas is given by:
1) nR(Vf - Vi)
2) nR ln(Vf - Vi)
3) nR ln(Vi/Vf )
4) nR ln(Vf/Vi)
5) none of the above
Q28) One mole of an ideal gas expands reversibly and isothermally
at temperature T until its volume is doubled. The change of
entropy of this gas for this process is:
1) Rln 2
2) (ln 2)/T
3) 0
4) RT ln 2
5) 2R
Q29) Twenty-five identical molecules are in a box. Microstates are
designated by identifying the molecules in the left and right halves
of the box. The multiplicity of the configuration with 15 molecules
in the right half and 10 molecules in the left half is:
1) 1.03  1023
2) 3.27  106
3) 150
4) 25
5) 5
Q30) Twenty-five identical molecules are in a box. Microstates are
designated by identifying the molecules in the left and right halves
of the box. The Boltzmann constant is 1.38  10-23 J/K. The
entropy associated with the configuration for which 15 molecules
are in the left half and 10 molecules are in the right half is:
1) 2.07  10-22 J/K
4) 6.91  10-23 J/K
2) 7.31  10-22 J/K
5) 2.22  10-23 J/K
3) 4.44  10-23 J/K