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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