MDCAT Thermochemistry MCQs

This comprehensive set of MCQs on Thermochemistry is designed to cover all essential topics required for success in the Medical and Dental College Admission Test (MDCAT). Focused on key concepts such as heat transfer, enthalpy, and the energy changes during chemical reactions, these MCQs are crafted to help aspiring medical and dental students build a strong understanding of thermochemistry and its applications in health sciences.

Who should practice Thermochemistry MCQs?

Students preparing for the MDCAT who wish to deepen their understanding of the energy changes in chemical reactions and their impact on reaction spontaneity and equilibrium.
Individuals seeking to enhance their knowledge of key topics such as exothermic and endothermic reactions, bond dissociation energy, and calorimetry, which are important for various medical and dental disciplines.
University students targeting high-yield topics like Hess’s Law, enthalpy of formation, and Gibbs free energy.
Anyone aiming to build a deeper understanding of how thermochemical principles apply to metabolic reactions and physiological processes.
Candidates focused on developing problem-solving skills related to the energy dynamics of chemical reactions.
Suitable for all students preparing for the MDCAT, including those looking to improve their exam confidence in thermochemistry and better understand its role in chemical reactions.

1. In thermodynamics, which of the following is considered a “system”?

A) The entire universe
B) The part of the universe under study
C) The surroundings of the experiment
D) The heat energy only

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2. What is the term used to define everything in the universe except the system?

A) Energy
B) Enthalpy
C) Surroundings
D) Heat

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3. A state function is a property that depends on:

A) The path taken to reach a specific state
B) The initial and final states only
C) The amount of heat added
D) The speed of the process

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4. Which of the following is a state function?

A) Work
B) Heat
C) Enthalpy
D) Distance

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5. The standard state of a substance is defined at:

A) 25°C and 1 atm pressure
B) 100°C and 1 atm pressure
C) 0°C and 1 atm pressure
D) 25°C and 2 atm pressure

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6. What is the standard enthalpy change of a reaction?

A) The enthalpy change measured at non-standard conditions
B) The enthalpy change measured at standard conditions
C) The energy released during a reaction
D) The heat required to break bonds

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7. The term “enthalpy” refers to:

A) The total energy of a system
B) The heat content of a system at constant pressure
C) The energy required to heat 1 mole of a substance
D) The energy used in chemical reactions

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8. The first law of thermodynamics states that:

A) Energy can be created but not destroyed
B) Energy can neither be created nor destroyed, only transformed
C) Heat energy is always lost in reactions
D) The energy of the universe is constant

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9. In an endothermic reaction, the sign of ΔH is:

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

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10. Which of the following best describes an exothermic reaction?

A) The system absorbs heat
B) The system releases heat
C) The system remains at a constant temperature
D) The reaction only occurs at high pressure

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11. The heat content of a reaction is represented by which symbol?

A) ΔE
B) ΔH
C) ΔS
D) ΔG

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12. If the enthalpy change for a reaction is negative, the reaction is:

A) Endothermic
B) Exothermic
C) Non-spontaneous
D) Reversible

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13. Hess’s law states that the total enthalpy change for a reaction is:

A) Dependent on the steps taken
B) The same, regardless of the pathway
C) Always positive
D) Zero for spontaneous reactions

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14. Which of the following is true according to Hess’s law?

A) The heat of formation is path dependent
B) The overall enthalpy change is independent of the reaction steps
C) The heat of combustion always equals zero
D) The heat released in an exothermic process is never spontaneous

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15. Enthalpy of formation refers to:

A) The heat absorbed when a compound is decomposed
B) The heat change when one mole of a compound is formed from its elements
C) The total heat absorbed during a chemical reaction
D) The heat lost by a system to the surroundings

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16. When heat is added to a system, which of the following can increase?

A) Internal energy
B) Surrounding temperature
C) Chemical potential
D) Surrounding pressure

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17. The heat of combustion is defined as:

A) The heat released when one mole of a substance is burned in excess oxygen
B) The heat absorbed during the formation of a compound
C) The energy required to break chemical bonds
D) The heat content of a system

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18. If a system does work on the surroundings, the internal energy of the system:

A) Increases
B) Decreases
C) Remains the same
D) Doubles

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19. The surroundings perform work on the system in which type of reaction?

A) Exothermic
B) Endothermic
C) Isothermal
D) Isobaric

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20. The heat required to raise the temperature of 1 gram of a substance by 1°C is called:

A) Specific heat
B) Enthalpy
C) Heat capacity
D) Calorimetry

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21. A chemical reaction that occurs without any continuous input of energy is considered:

A) Endothermic
B) Spontaneous
C) Non-spontaneous
D) Exergonic

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22. The enthalpy change for an exothermic reaction is always:

A) Greater than zero
B) Less than zero
C) Equal to zero
D) Unpredictable

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23. For an endothermic reaction, the energy absorbed is:

A) Transferred to the surroundings
B) Stored in the chemical bonds
C) Released as heat
D) Irrelevant to the surroundings

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24. Which of the following is an example of a state function?

A) Work
B) Heat
C) Enthalpy
D) Distance

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25. The first law of thermodynamics is also known as the law of:

A) Energy conservation
B) Energy transfer
C) Heat exchange
D) Spontaneity

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26. When a chemical reaction occurs at constant pressure, the heat change is equal to:

A) ΔE
B) ΔS
C) ΔH
D) ΔG

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27. The specific heat of a substance is defined as:

A) The heat required to raise the temperature of 1 mole by 1°C
B) The heat required to raise the temperature of 1 gram by 1°C
C) The total heat content of the substance
D) The heat released during a chemical reaction

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28. The change in enthalpy (ΔH) for a reaction can be calculated using:

A) Hess’s law
B) The specific heat capacity
C) The ideal gas law
D) The rate constant

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29. A reaction that absorbs heat from its surroundings is called:

A) Exothermic
B) Endothermic
C) Isothermal
D) Spontaneous

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30. Which of the following is not a thermodynamic state function?

A) Enthalpy
B) Pressure
C) Volume
D) Work

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31. The enthalpy change for a reaction at constant temperature and pressure can be determined using:

A) The heat capacity
B) The calorimeter
C) The equilibrium constant
D) The rate constant

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32. If the enthalpy change for a reaction is +150 kJ/mol, the reaction is:

A) Exothermic
B) Endothermic
C) Spontaneous
D) Irreversible

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33. In an exothermic reaction, the products have:

A) Higher enthalpy than the reactants
B) Lower enthalpy than the reactants
C) The same enthalpy as the reactants
D) Unpredictable enthalpy

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34. The energy needed to initiate a chemical reaction is called:

A) Enthalpy
B) Activation energy
C) Standard state
D) Heat of reaction

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35. A process in which the enthalpy of the products is less than that of the reactants is termed:

A) Endothermic
B) Exothermic
C) Isothermal
D) Adiabatic

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36. If a chemical reaction releases energy, it is categorized as:

A) Endothermic
B) Exothermic
C) Isothermal
D) Reversible

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37. When calculating ΔH using Hess’s law, the enthalpy changes of individual steps must:

A) Always be added together
B) Be averaged
C) Be subtracted
D) Be multiplied

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38. Which of the following is a characteristic of an isothermal process?

A) Temperature remains constant
B) Pressure remains constant
C) Volume remains constant
D) Enthalpy remains constant

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39. In thermodynamics, a “spontaneous” process is one that:

A) Requires continuous energy input
B) Occurs naturally without external influence
C) Can be reversed easily
D) Involves a decrease in entropy

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40. The term “heat of fusion” refers to:

A) The energy required to vaporize a substance
B) The energy required to melt a substance
C) The energy released when a substance freezes
D) The energy change during a chemical reaction

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41. Which statement is true about the heat capacity of water?

A) It is low compared to most substances
B) It is high, making water effective for temperature regulation
C) It is zero
D) It varies significantly with temperature

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42. When a system does work on the surroundings, the internal energy change (ΔE) is:

A) Positive
B) Negative
C) Unchanged
D) Indeterminate

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43. In an adiabatic process, heat exchange with the surroundings is:

A) Large
B) Small
C) Zero
D) High

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44. Which of the following represents a thermodynamic cycle?

A) Any process involving heat transfer
B) A series of reactions returning to the initial state
C) A process with constant pressure
D) A reaction with a negative ΔH

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45. The enthalpy change for the formation of one mole of a compound from its elements in their standard states is called:

A) Heat of fusion
B) Heat of vaporization
C) Standard enthalpy of formation
D) Heat of combustion

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46. The enthalpy of a reaction can be determined using which of the following?

A) Calorimetry
B) Chromatography
C) Titration
D) Filtration

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47. In the context of thermodynamics, “ΔG” represents:

A) Change in enthalpy
B) Change in Gibbs free energy
C) Change in internal energy
D) Change in entropy

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48. If ΔG is negative for a reaction, it indicates that the reaction is:

A) Non-spontaneous
B) Spontaneous
C) At equilibrium
D) Endothermic

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49. The total heat content of the reactants and products in a chemical reaction is known as:

A) Entropy
B) Enthalpy
C) Energy
D) Temperature

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50. Which process is always exothermic?

A) Freezing of water
B) Melting of ice
C) Vaporization of liquid
D) Sublimation of dry ice

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51. The standard enthalpy change of a reaction can be affected by changes in:

A) Temperature
B) Pressure
C) Concentration of reactants
D) All of the above

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52. The First Law of Thermodynamics states that:

A) Energy cannot be created or destroyed
B) Entropy of an isolated system always increases
C) Heat flows from cold to hot spontaneously
D) All processes are reversible

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53. The term “enthalpy of vaporization” refers to:

A) The energy required to condense a gas into a liquid
B) The energy required to boil a liquid into a gas
C) The energy released during freezing
D) The energy change during a chemical reaction

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54. Which of the following statements about Hess’s law is true?

A) It applies only to gaseous reactions
B) It is only applicable at constant pressure
C) The total enthalpy change is independent of the pathway
D) It cannot be used for reactions in solution

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55. The enthalpy change of a reaction can be expressed in terms of:

A) Heat absorbed or released at constant volume
B) Heat absorbed or released at constant pressure
C) Change in kinetic energy
D) Change in gravitational potential energy

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56. If ΔH for a reaction is -75 kJ, it means that:

A) 75 kJ of energy is absorbed
B) 75 kJ of energy is released
C) The reaction is at equilibrium
D) The reaction has no energy change

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57. The relationship between ΔH, ΔE, and work (w) can be expressed as:

A) ΔH = ΔE + w
B) ΔH = ΔE – w
C) ΔH = ΔE + PΔV
D) ΔH = ΔE – PΔV

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58. The enthalpy change when one mole of a substance is completely burned in oxygen is known as:

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

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59. Which of the following statements about state functions is true?

A) Their value depends on the path taken to reach a specific value
B) They are independent of the history of the system
C) They can only be measured at equilibrium
D) They do not change during a reversible process

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60. When calculating the change in enthalpy using Hess’s law, which of the following is necessary?

A) Identifying the reactants and products
B) Using standard enthalpy values
C) Ensuring that the equations are balanced
D) All of the above

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61. The process of dissolving a solute in a solvent that releases heat is known as:

A) Endothermic dissolution
B) Exothermic dissolution
C) Isothermal dissolution
D) Adiabatic dissolution

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62. The change in enthalpy when a chemical reaction occurs at constant pressure is called:

A) ΔE
B) ΔG
C) ΔH
D) ΔS

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63. A reaction with a positive ΔH value is generally classified as:

A) Spontaneous
B) Non-spontaneous
C) Exothermic
D) Isothermal

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64. The efficiency of a heat engine can be calculated by the ratio of:

A) Work output to heat input
B) Heat output to work input
C) Heat input to work output
D) None of the above

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65. A process that absorbs heat from its surroundings can be classified as:

A) Exothermic
B) Endothermic
C) Isothermal
D) Spontaneous

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66. The heat absorbed or released during a chemical reaction is referred to as:

A) Enthalpy
B) Specific heat
C) Calorimetry
D) Gibbs free energy

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67. In a reversible process, the system:

A) Cannot return to its original state
B) Can return to its original state without changes in surroundings
C) Always increases in entropy
D) Always decreases in entropy

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68. The sign of ΔH for an exothermic reaction is:

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

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69. According to the First Law of Thermodynamics, energy:

A) Can be created or destroyed
B) Can only be transformed from one form to another
C) Cannot be transformed
D) Is always conserved in isolated systems

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70. A system at equilibrium has:

A) No energy exchange with the surroundings
B) Constant temperature
C) Constant concentrations of reactants and products
D) Constant enthalpy

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71. The term “enthalpy of fusion” refers to:

A) The energy required to boil a liquid into a gas
B) The energy released when a gas condenses into a liquid
C) The energy required to melt a solid into a liquid
D) The energy change during a chemical reaction

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72. Which of the following is a characteristic of a spontaneous process?

A) It occurs without external intervention
B) It requires constant energy input
C) It is always exothermic
D) It results in a decrease in entropy

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73. The specific heat of a substance is defined as:

A) The amount of heat needed to raise the temperature of 1 gram of the substance by 1°C
B) The heat released during a chemical reaction
C) The heat absorbed during a phase change
D) The total heat content of a substance

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74. The standard state of a substance at 1 atm pressure and 25°C is referred to as:

A) Standard temperature and pressure (STP)
B) Standard conditions for temperature and pressure (SCTP)
C) Standard enthalpy
D) Standard state

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75. According to Hess’s law, the total enthalpy change of a reaction is:

A) Equal to the sum of the enthalpy changes of the individual steps
B) Always zero
C) Dependent on the rate of the reaction
D) Only applicable to exothermic reactions

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76. In the context of thermochemistry, “system” refers to:

A) The surroundings of a chemical reaction
B) The specific part of the universe being studied
C) Any energy exchange with the surroundings
D) The energy released during a reaction

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77. Which of the following represents an endothermic reaction?

A) Combustion of gasoline
B) Dissolving ammonium nitrate in water
C) Neutralization of an acid with a base
D) Condensation of steam

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78. The unit of enthalpy change in the SI system is:

A) Joules per mole
B) Kilojoules
C) Calories
D) Liters

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79. The Gibbs free energy change (ΔG) is related to enthalpy change (ΔH) and entropy change (ΔS) by the equation:

A) ΔG = ΔH + TΔS
B) ΔG = ΔH – TΔS
C) ΔG = ΔH + ΔS
D) ΔG = ΔH – ΔS

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80. When calculating the enthalpy change using the standard enthalpy of formation, what is the key requirement?

A) All reactants and products must be in their standard states
B) Only gaseous reactants are allowed
C) The reaction must be exothermic
D) It must occur at constant pressure

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81. The enthalpy change for a reaction can be calculated from:

A) The amount of products formed only
B) The amount of reactants consumed only
C) The enthalpy of formation of the reactants and products
D) The temperature change only

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82. The concept of state functions in thermodynamics implies that:

A) Their value depends on the path taken
B) They are independent of the history of the system
C) They can only be defined for gaseous systems
D) They can only be measured at high temperatures

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83. Which of the following reactions is an example of Hess’s law application?

A) Determining the heat of formation of glucose
B) Calculating the rate of a reaction
C) Finding the activation energy of a reaction
D) Measuring temperature changes in a solution

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84. In thermodynamics, “surroundings” refers to:

A) The chemical reaction itself
B) Everything outside the system being studied
C) The heat released during a reaction
D) The phase changes of substances

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85. The enthalpy change for an exothermic reaction is generally:

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

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86. The enthalpy of a reaction can be determined using:

A) Calorimetry
B) Thermocouples
C) pH indicators
D) Titration

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87. In a calorimetry experiment, if the temperature of the surroundings increases, the reaction is likely:

A) Endothermic
B) Exothermic
C) Isothermal
D) Non-spontaneous

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88. The change in enthalpy during a phase change at constant temperature is:

A) Positive only
B) Negative only
C) Zero
D) Dependent on the specific heat

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89. The relationship between the standard enthalpy changes of a reaction and its components can be summarized by:

A) The heat capacity equation
B) The enthalpy of formation equation
C) The Hess’s law equation
D) The Gibbs free energy equation

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90. A reaction in which the products have a lower enthalpy than the reactants is:

A) Endothermic
B) Exothermic
C) Isothermal
D) Reversible

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91. Which of the following statements about the First Law of Thermodynamics is correct?

A) Energy can be created or destroyed
B) Energy can be transformed from one form to another
C) Energy is always lost during a reaction
D) The total energy of an isolated system decreases

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92. If a chemical reaction has a negative ΔH, it is classified as:

A) Endothermic
B) Exothermic
C) Isothermal
D) Adiabatic

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93. In an endothermic reaction, the sign of ΔH is:

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

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94. The term “enthalpy change” during a reaction is defined as:

A) The difference in internal energy
B) The heat absorbed or released at constant pressure
C) The temperature change of the surroundings
D) The work done by the system

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95. Which of the following is an example of a state function?

A) Work
B) Heat
C) Enthalpy
D) Time

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96. The enthalpy of reaction is typically expressed in units of:

A) Grams
B) Liters
C) Joules per mole
D) Moles

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97. The enthalpy change for the formation of water is often used to illustrate:

A) The kinetic energy of particles
B) The standard enthalpy of formation
C) The specific heat capacity of water
D) The ideal gas law

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98. Hess’s law allows us to calculate the enthalpy change for a reaction by:

A) Measuring the heat of products only
B) Summing the enthalpy changes of individual steps
C) Determining the concentration of reactants
D) Monitoring the pressure changes during a reaction

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99. When a reaction occurs in a closed container, the energy change associated with the reaction is usually measured as:

A) Enthalpy change
B) Work done
C) Temperature change
D) Pressure change

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100. The term “enthalpy of reaction” refers to:

A) The energy required to initiate a reaction
B) The heat change that occurs during a chemical reaction
C) The energy lost during a reaction
D) The total energy in the system

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