MDCAT Thermodynamics MCQs

This comprehensive set of MCQs on Thermodynamics is designed to cover all essential topics required for success in the Medical and Dental College Admission Test (MDCAT). Focused on key subjects such as the Laws of Thermodynamics, Heat Transfer, Work, Enthalpy, and Thermodynamic Processes, these MCQs are crafted to help aspiring medical and dental students build a solid understanding of thermodynamic principles and their applications in health sciences.

Who should practice Thermodynamics MCQs?

Students preparing for the MDCAT who wish to deepen their understanding of thermodynamic concepts, which are vital for various biochemical and physiological processes.
Individuals seeking to enhance their knowledge of energy transfer, efficiency, and the role of thermodynamics in metabolic reactions, crucial for medical and dental disciplines.
University students targeting high-yield topics such as thermodynamic cycles, phase changes, and their implications for the design of medical technologies.
Anyone aiming to strengthen their foundational understanding of thermodynamics and its applications in health, disease mechanisms, and environmental science.
Candidates focused on developing critical thinking and analytical skills related to thermodynamic equations and problem-solving in real-world scenarios.

1. What does the first law of thermodynamics state?

A) Energy can be created or destroyed
B) Energy can be transformed but not created or destroyed
C) Energy is always conserved
D) Heat flows from cold to hot

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2. Which of the following is a unit of specific heat capacity?

A) Joules per kilogram
B) Joules per kilogram per degree Celsius
C) Joules per mole
D) Calories per mole

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3. If a system does 50 J of work and absorbs 20 J of heat, what is the change in internal energy?

A) -30 J
B) 20 J
C) 70 J
D) -50 J

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4. Which of the following equations represents the first law of thermodynamics?

A) ΔU = Q + W
B) ΔU = Q – W
C) ΔU = W – Q
D) ΔU = Q + ΔH

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5. What does the symbol ‘Q’ represent in thermodynamics?

A) Work done by the system
B) Heat added to the system
C) Change in internal energy
D) Pressure of the system

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6. When heat is added to a system at constant volume, the internal energy will…

A) Decrease
B) Increase
C) Stay the same
D) Become zero

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7. Which law states that the total energy of an isolated system is constant?

A) Zeroth Law of Thermodynamics
B) First Law of Thermodynamics
C) Second Law of Thermodynamics
D) Third Law of Thermodynamics

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8. In which process does the internal energy remain constant?

A) Isobaric
B) Isochoric
C) Isothermal
D) Adiabatic

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9. Which of the following correctly defines molar specific heat at constant volume (Cv)?

A) Heat required to raise the temperature of one mole of a substance by one degree Celsius at constant pressure
B) Heat required to raise the temperature of one mole of a substance by one degree Celsius at constant volume
C) Heat released when one mole of a substance condenses
D) Heat required to change one mole of a substance from solid to liquid

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10. What happens to the internal energy of an ideal gas during an isothermal expansion?

A) It decreases
B) It increases
C) It remains constant
D) It becomes negative

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11. The heat capacity of a substance is defined as…

A) The amount of heat needed to change its temperature by one degree
B) The heat required to change its phase
C) The heat needed to raise the temperature of the substance to boiling
D) The heat needed to change one mole of a substance from solid to gas

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12. If the specific heat of water is 4.18 J/g°C, how much heat is needed to raise the temperature of 100 g of water from 20°C to 30°C?

A) 418 J
B) 4180 J
C) 41.8 J
D) 41800 J

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13. Which of the following processes is adiabatic?

A) Constant temperature
B) Constant pressure
C) No heat exchange
D) Heat is absorbed

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14. Which quantity represents the change in internal energy of a closed system?

A) Q + W
B) Q – W
C) W – Q
D) 0

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15. What does ‘ΔU’ signify in thermodynamics?

A) Change in work
B) Change in heat
C) Change in internal energy
D) Change in pressure

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16. During a phase change, what happens to the temperature of a substance?

A) It increases
B) It decreases
C) It remains constant
D) It fluctuates

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17. What is the molar specific heat of an ideal gas at constant pressure (Cp)?

A) Cv + R
B) Cv – R
C) Cv + 2R
D) Cv

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18. Which of the following statements about the first law of thermodynamics is true?

A) Energy can be created
B) Energy can be destroyed
C) Energy can only change forms
D) Energy is not conserved

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19. What is the value of R (the ideal gas constant) in J/(mol·K)?

A) 8.314
B) 0.0821
C) 0.8314
D) 8.314 × 10^3

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20. In a cyclic process, the change in internal energy is…

A) Positive
B) Negative
C) Zero
D) Dependent on work done

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21. Which of the following describes an isothermal process?

A) Constant pressure
B) Constant volume
C) Constant temperature
D) No heat exchange

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22. If a gas expands and does work on the surroundings, what happens to the internal energy of the gas?

A) Increases
B) Decreases
C) Remains constant
D) Becomes negative

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23. The heat capacity of a substance depends on…

A) Its mass only
B) Its temperature only
C) Its phase
D) All of the above

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24. What is the relationship between Cp and Cv for an ideal gas?

A) Cp = Cv
B) Cp = Cv + R
C) Cp = Cv – R
D) Cp = Cv × R

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25. Which process occurs without heat transfer to or from the surroundings?

A) Isothermal
B) Isochoric
C) Adiabatic
D) Isobaric

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26. Which thermodynamic cycle is used in heat engines?

A) Carnot Cycle
B) Refrigeration Cycle
C) Rankine Cycle
D) Brayton Cycle

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27. What is the principle behind a heat engine?

A) To convert thermal energy into mechanical work
B) To absorb heat only
C) To produce heat
D) To change the phase of a substance

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28. Which of the following statements is true for a perfectly insulated system?

A) Q = 0
B) W = 0
C) ΔU = 0
D) Both Q and W = 0

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29. The specific heat of air is approximately…

A) 1.005 J/g°C
B) 2.093 J/g°C
C) 4.18 J/g°C
D) 0.5 J/g°C

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30. In which of the following scenarios does the system absorb heat?

A) Exothermic reaction
B) Endothermic reaction
C) Isothermal expansion
D) Adiabatic process

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31. Which law describes the relationship between heat transfer and work done in a thermodynamic system?

A) Zeroth Law
B) First Law
C) Second Law
D) Third Law

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32. What does the term “work done on the system” mean?

A) Energy is lost
B) Energy is gained
C) No energy change occurs
D) Energy is converted to heat

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33. The latent heat of fusion is…

A) The heat required to change a solid into a liquid
B) The heat required to change a liquid into a gas
C) The heat required to change a gas into a liquid
D) The heat required to change a solid into a gas

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34. How is heat capacity affected by the mass of the substance?

A) It decreases with mass
B) It increases with mass
C) It remains the same regardless of mass
D) It varies unpredictably

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35. What type of process is described when heat is added to a system and the volume does not change?

A) Isothermal
B) Isobaric
C) Isochoric
D) Adiabatic

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36. In a reversible process, the system is…

A) Always at equilibrium
B) Never at equilibrium
C) Always expanding
D) Always contracting

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37. What does a positive value for work indicate?

A) Work is done by the system
B) Work is done on the system
C) No work is done
D) Work is not defined

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38. The change in temperature is directly proportional to…

A) Heat transfer
B) Work done
C) Volume change
D) Pressure change

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39. Which of the following factors does NOT affect the heat capacity of a substance?

A) Pressure
B) Mass
C) Phase
D) Chemical composition

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40. The process of heating a gas at constant volume leads to…

A) Decreased pressure
B) Increased temperature
C) Increased work done
D) Decreased internal energy

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41. What is the molar specific heat capacity of an ideal monatomic gas at constant volume?

A) (3/2)R
B) (5/2)R
C) 2R
D) R

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42. Which type of thermodynamic process involves both heat transfer and work done?

A) Isochoric
B) Isothermal
C) Adiabatic
D) Isobaric

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43. The second law of thermodynamics is primarily concerned with…

A) Energy conservation
B) Entropy
C) Heat transfer
D) Phase changes

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44. What happens to the entropy of the universe in a spontaneous process?

A) It decreases
B) It remains constant
C) It increases
D) It fluctuates

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45. Which statement is true for an ideal gas?

A) It occupies no volume
B) It has attractive forces between molecules
C) Its internal energy depends on temperature only
D) It can exist as a liquid

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46. When heat is added to a substance during a phase change, what happens to its temperature?

A) It decreases
B) It remains constant
C) It increases
D) It fluctuates

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47. Which of the following represents an isobaric process?

A) Gas expands at constant temperature
B) Gas is compressed with constant pressure
C) Gas is heated with constant volume
D) Gas cools at constant volume

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48. What is the latent heat of vaporization?

A) The heat required to convert a solid into a liquid
B) The heat required to convert a liquid into a gas
C) The heat required to convert a gas into a liquid
D) The heat required to convert a solid into a gas

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49. In an adiabatic process, which statement is true?

A) Heat is absorbed from the surroundings
B) Heat is released to the surroundings
C) No heat is exchanged with the surroundings
D) Temperature remains constant

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50. Which of the following is an example of an exothermic process?

A) Melting ice
B) Burning wood
C) Evaporating water
D) Subliming dry ice

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51. What is the primary factor that determines the specific heat capacity of a substance?

A) The molecular structure
B) The size of the container
C) The amount of substance present
D) The pressure applied

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52. The heat required to raise the temperature of 1 kg of water by 1°C is known as…

A) Calorie
B) Joule
C) Kilocalorie
D) BTU

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53. If a system does 100 J of work and loses 40 J of heat, what is the change in internal energy?

A) -60 J
B) 60 J
C) 40 J
D) -40 J

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54. Which thermodynamic process has no change in pressure?

A) Isothermal
B) Isochoric
C) Isobaric
D) Adiabatic

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55. The heat absorbed or released during a phase change is called…

A) Sensible heat
B) Latent heat
C) Specific heat
D) Thermal energy

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56. The efficiency of a Carnot engine depends on…

A) The temperature of the hot reservoir
B) The temperature of the cold reservoir
C) Both A and B
D) The work output

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57. Which of the following statements is true regarding specific heat capacity?

A) It is always constant for a substance
B) It varies with temperature and pressure
C) It depends only on the phase of the substance
D) It is independent of the amount of substance

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58. What is the change in internal energy for an isothermal process of an ideal gas?

A) Positive
B) Negative
C) Zero
D) Undefined

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59. What does the term “enthalpy” refer to in thermodynamics?

A) Internal energy plus pressure times volume
B) Internal energy minus pressure times volume
C) Heat content at constant pressure
D) Change in heat content

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60. In a closed system, if the heat added is greater than the work done, what can be said about the change in internal energy?

A) It is negative
B) It is zero
C) It is positive
D) It cannot be determined

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61. The term “heat engine” is best described as…

A) A device that converts heat into work
B) A device that absorbs heat only
C) A device that transfers heat
D) A device that cools down a substance

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62. The formula Q = mcΔT is used to calculate…

A) Heat transfer during phase changes
B) The heat required to change temperature
C) Work done in an isothermal process
D) Total energy in a thermodynamic system

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63. The process where the pressure of a gas remains constant while it is heated is called…

A) Isothermal process
B) Isochoric process
C) Isobaric process
D) Adiabatic process

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64. In a thermodynamic process, the efficiency can be defined as the ratio of…

A) Work done to heat absorbed
B) Heat absorbed to work done
C) Work done to heat rejected
D) Heat rejected to work done

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65. The change in entropy during a reversible process is…

A) Positive
B) Negative
C) Zero
D) Can be either positive or negative

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66. The specific heat capacity of a substance generally increases with…

A) Increase in pressure
B) Increase in temperature
C) Increase in volume
D) Decrease in mass

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67. In which process does the volume of the gas remain constant?

A) Isothermal
B) Isobaric
C) Isochoric
D) Adiabatic

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68. The molar heat capacity at constant pressure (Cp) for a diatomic gas is approximately…

A) 3R/2
B) 5R/2
C) 7R/2
D) 9R/2

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69. Which statement about heat transfer is true?

A) Heat flows from cold to hot
B) Heat flows from hot to cold
C) Heat does not flow
D) Heat can flow without temperature difference

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70. In thermodynamics, “work” is defined as…

A) Energy transferred due to a temperature difference
B) Energy transferred due to force acting over a distance
C) Energy stored in a system
D) Energy released during a phase change

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71. The heat required to raise the temperature of one mole of a substance by one degree Celsius at constant volume is known as…

A) Molar heat capacity
B) Molar enthalpy
C) Molar entropy
D) Molar thermal conductivity

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72. The unit of specific heat capacity is…

A) J/g°C
B) J/kg
C) J/K
D) J/mol

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73. In which process does a gas expand and do work on the surroundings?

A) Isothermal expansion
B) Isochoric expansion
C) Adiabatic expansion
D) Isobaric expansion

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74. What is the primary role of a heat exchanger?

A) To increase temperature
B) To decrease pressure
C) To transfer heat between fluids
D) To convert heat to work

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75. The principle of conservation of energy in thermodynamics states that…

A) Energy can be created
B) Energy can be destroyed
C) Energy can be transformed but not created or destroyed
D) Energy does not change form

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76. In an ideal gas, the internal energy depends on…

A) Volume and pressure
B) Temperature only
C) Temperature and pressure
D) Volume only

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77. During an isothermal expansion of an ideal gas, what remains constant?

A) Pressure
B) Volume
C) Temperature
D) Internal energy

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78. The heat required to change the temperature of a substance is known as…

A) Sensible heat
B) Latent heat
C) Total heat
D) Specific heat

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79. Which of the following statements is true about an adiabatic process?

A) Heat is transferred from the surroundings
B) Work done on the system increases internal energy
C) Temperature remains constant
D) No work is done

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80. In which process is the temperature of the system raised without heat exchange?

A) Isothermal
B) Isochoric
C) Adiabatic
D) Isobaric

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81. The Clausius-Clapeyron equation describes the relationship between…

A) Pressure and volume
B) Pressure and temperature
C) Temperature and heat
D) Entropy and heat

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82. The heat capacity of a substance is defined as…

A) The amount of heat needed to change its temperature by a specific amount
B) The total energy stored in the substance
C) The energy required to change its phase
D) The energy released during combustion

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83. Which of the following is NOT a state function?

A) Internal energy
B) Enthalpy
C) Work
D) Entropy

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84. In a cyclic process, the change in internal energy is…

A) Positive
B) Negative
C) Zero
D) Undefined

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85. Which law states that energy cannot be created or destroyed?

A) First law of thermodynamics
B) Second law of thermodynamics
C) Third law of thermodynamics
D) Zeroth law of thermodynamics

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86. The heat absorbed during the melting of a solid is known as…

A) Heat of fusion
B) Heat of vaporization
C) Heat of sublimation
D) Heat of combustion

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87. The value of R (universal gas constant) in J/(mol·K) is approximately…

A) 8.314
B) 0.0821
C) 8.314 x 10⁻³
D) 0.001987

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88. The ideal gas law is represented by which of the following equations?

A) PV = nRT
B) PV = nRT²
C) PV = n²RT
D) PV = n/R

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89. The concept of “absolute zero” refers to…

A) 0°C
B) 0°F
C) 0 K
D) -273°C

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90. In a thermodynamic cycle, the net work done is equal to…

A) The heat added to the system
B) The heat removed from the system
C) The difference between heat added and work done
D) The sum of all heat transfers

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91. The Joule-Thomson effect describes…

A) Temperature change due to pressure change in a gas
B) Temperature change due to heat exchange
C) Temperature change during a phase change
D) Temperature change due to volume change

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92. The heat required to raise the temperature of a substance is directly proportional to…

A) The amount of substance
B) The specific heat capacity
C) The change in temperature
D) All of the above

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93. The term “system” in thermodynamics refers to…

A) The surroundings of a reaction
B) The part of the universe under study
C) The energy exchanged
D) The state functions involved

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94. Which of the following statements is true regarding an isothermal process?

A) The internal energy changes
B) The temperature remains constant
C) Work done is zero
D) Heat exchange is not involved

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95. The term “latent heat” refers to the heat required for…

A) Temperature changes
B) Phase changes
C) Chemical reactions
D) Work done

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96. In thermodynamics, an “open system” is defined as one that can exchange…

A) Energy only
B) Matter only
C) Both energy and matter
D) Neither energy nor matter

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97. The efficiency of a heat engine is defined as the ratio of…

A) Work output to heat input
B) Heat output to work input
C) Work input to heat output
D) Heat absorbed to work rejected

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98. The term “work done by the system” can be calculated using…

A) W = PΔV
B) W = ΔPΔV
C) W = mgh
D) W = Fd

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99. In a reversible isothermal expansion, the work done by the gas is given by which equation?

A) W = nRT ln(Vf/Vi)
B) W = nRT (Vf – Vi)
C) W = PΔV
D) W = mgh

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100. The concept of “enthalpy” is particularly useful in analyzing…

A) Chemical reactions at constant pressure
B) Reactions in an isolated system
C) Work done by a gas
D) All of the above

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