Thermochemistry and Energetics of Chemical Reactions

21 free MDCAT Chemistry MCQs on Thermochemistry and Energetics of Chemical Reactions (PM&DC syllabus), each with the answer, an explanation and the textbook line it comes from. Tap to check, no sign-up.

Tap an answer to check it · 21 questions

1. Question 1

   The bond dissociation energy of the H-H bond is:
   • A348 kJ/mol
   • B499 kJ/mol
   • C242 kJ/mol
   • D436 kJ/mol
   Show answer and explanation

   Answer: D) 436 kJ/mol

   499 kJ/mol is for O2; 242 kJ/mol is the dissociation energy of Cl2 used in the Born-Haber cycle. Source: Chemistry 11 KPK (taleem360.com), p. 349.

2. Question 2

   The specific heat of water is:
   • A4.184 J g-1 K-1
   • B0.418 J g-1 K-1
   • C41.84 J g-1 K-1
   • D1.184 J g-1 K-1
   Show answer and explanation

   Answer: A) 4.184 J g-1 K-1

   Heat capacity of 50 g water = 50 x 4.184 = 209.2 J/K. Source: Chemistry 11 KPK (taleem360.com), p. 349.

3. Question 3

   Standard enthalpy changes are measured at:
   • A273 K and one atmosphere
   • B298 K and one atmosphere
   • C298 K and two atmospheres
   • D373 K and one atmosphere
   Show answer and explanation

   Answer: B) 298 K and one atmosphere

   298 K is 25 C; all substances are in their normal, natural states. Source: Chemistry 11 KPK (taleem360.com), p. 346.

4. Question 4

   To estimate food energy, grams of carbohydrate, protein and fat are multiplied respectively by:
   • A4, 4 and 4 kcal
   • B9, 4 and 4 kcal
   • C4, 9 and 4 kcal
   • D4, 4 and 9 kcal
   Show answer and explanation

   Answer: D) 4, 4 and 9 kcal

   Fat gives more than twice the energy per gram of carbohydrate or protein. Source: Chemistry 11 KPK (taleem360.com), p. 348.

5. Question 5

   The total heat content of a system, defined by H = E + PV, is its:
   • ASpecific heat
   • BInternal energy
   • CHeat capacity
   • DEnthalpy
   Show answer and explanation

   Answer: D) Enthalpy

   Enthalpy is a state function because E, P and V are. Source: Chemistry 11 KPK (taleem360.com), p. 345.

6. Question 6

   The heat change when one mole of a compound is formed from its elements in their standard states is the standard enthalpy of:
   • AFormation
   • BCombustion
   • CNeutralization
   • DAtomization
   Show answer and explanation

   Answer: A) Formation

   e.g. C(graphite) + O2 -> CO2, -393.51 kJ/mol. Source: Chemistry 11 KPK (taleem360.com), p. 347.

7. Question 7

   The heat produced when one mole of a substance is completely burnt in excess oxygen under standard conditions is the standard enthalpy of:
   • AFormation
   • BCombustion
   • CNeutralization
   • DSolution
   Show answer and explanation

   Answer: B) Combustion

   Heats of combustion are always negative (exothermic). Source: Chemistry 11 KPK (taleem360.com), p. 348.

8. Question 8

   The amount of heat required to raise the temperature of a given amount of a substance by 1 K is its:
   • AMolar heat capacity
   • BSpecific heat
   • CHeat capacity
   • DInternal energy
   Show answer and explanation

   Answer: C) Heat capacity

   Specific heat is per gram and molar heat capacity per mole; heat capacity (C = ms) is for the given amount. Source: Chemistry 11 KPK (taleem360.com), p. 349.

9. Question 9

   Which one of the following is NOT a state function?
   • AHeat
   • BEnthalpy
   • CTemperature
   • DPressure
   Show answer and explanation

   Answer: A) Heat

   Heat (like work) is a mode of energy transfer and depends on the path. Source: Chemistry 11 KPK (taleem360.com), p. 345.

10. Question 10

    For processes involving only solids and liquids, delta H is nearly equal to delta E because the:
    • AVolume change is very large
    • BVolume change is negligible
    • CHeat absorbed is zero
    • DPressure is very high
    Show answer and explanation

    Answer: B) Volume change is negligible

    With delta V close to zero, the P delta V term can be neglected. Source: Chemistry 11 KPK (taleem360.com), p. 345.

11. Question 11

    A snack contains 16 g carbohydrate, 7 g protein and 9 g fat. Its food energy is:
    • A201 kcal
    • B128 kcal
    • C173 kcal
    • D92 kcal
    Show answer and explanation

    Answer: C) 173 kcal

    16 x 4 + 7 x 4 + 9 x 9 = 64 + 28 + 81 = 173 kcal. Source: Chemistry 11 KPK (taleem360.com), p. 348.

12. Question 12

    One mole of an ideal gas expands from 15 dm3 to 20 dm3 against a constant external pressure of 2 atm. The work done is:
    • A70 atm dm3
    • B40 atm dm3
    • C2.5 atm dm3
    • D10 atm dm3
    Show answer and explanation

    Answer: D) 10 atm dm3

    w = P delta V = 2 atm x 5 dm3 = 10 atm dm3. Source: Chemistry 11 KPK (taleem360.com), p. 344.

13. Question 13

    For KBr: delta Hf = -405.8, sublimation of K = 88, half dissociation of Br2 = 96.25, IE of K = 414, EA of Br = -334.7 kJ/mol. Its lattice energy is:
    • A-669.3 kJ/mol
    • B-405.8 kJ/mol
    • C-1074.4 kJ/mol
    • D-142.3 kJ/mol
    Show answer and explanation

    Answer: A) -669.3 kJ/mol

    Born-Haber: LE = -405.8 - 88 - 414 - 96.25 - (-334.7) = -669.3 kJ/mol. Source: Chemistry 11 KPK (taleem360.com), p. 356.

14. Question 14

    Heat absorbed by a system at constant volume is used only to increase its:
    • AEnthalpy
    • BInternal energy
    • CVolume
    • DPressure
    Show answer and explanation

    Answer: B) Internal energy

    delta V = 0, so no work is done and delta E = qv. Source: Chemistry 11 KPK (taleem360.com), p. 344.

15. Question 15

    Heat absorbed or evolved at constant pressure is equal to the change in:
    • AWork done
    • BInternal energy
    • CEnthalpy
    • DHeat capacity
    Show answer and explanation

    Answer: C) Enthalpy

    qp = delta H, while qv = delta E. Source: Chemistry 11 KPK (taleem360.com), p. 345.

16. Question 16

    In chemistry, work done by the system on the surroundings is given the sign:
    • AEither sign
    • BPositive
    • CZero
    • DNegative
    Show answer and explanation

    Answer: D) Negative

    Work done on the system is positive; physics uses the opposite convention. Source: Chemistry 11 KPK (taleem360.com), p. 344.

17. Question 17

    The standard enthalpy of formation of O2(g) is:
    • AZero
    • B-393.5 kJ/mol
    • C+142.7 kJ/mol
    • D-285.8 kJ/mol
    Show answer and explanation

    Answer: A) Zero

    Elements in their most stable form are arbitrarily assigned zero. Source: Chemistry 11 KPK (taleem360.com), p. 347.

18. Question 18

    The heat of formation of CO is found indirectly by Hess's law because burning carbon in oxygen also forms:
    • AOzone
    • BCarbon dioxide
    • CWater
    • DMethane
    Show answer and explanation

    Answer: B) Carbon dioxide

    Side reactions prevent direct measurement. Source: Chemistry 11 KPK (taleem360.com), p. 353.

19. Question 19

    The heat of neutralization of any strong acid by any strong base is about the same because:
    • AThe same reaction occurs
    • BAll acids have equal mass
    • CWater is not formed
    • DNo heat is released
    Show answer and explanation

    Answer: A) The same reaction occurs

    Both are fully ionized, so the net reaction is always H+ + OH- -> H2O. Source: Chemistry 11 KPK (taleem360.com), p. 349.

20. Question 20

    Specific heat capacity is:
    • AAn extensive property
    • BAn intensive property
    • CA path function
    • DA form of work
    Show answer and explanation

    Answer: B) An intensive property

    It does not depend on quantity; heat capacity (C = ms) is extensive. Source: Chemistry 11 KPK (taleem360.com), p. 349.

21. Question 21

    The SI unit of thermal energy is the:
    • AErg
    • BCalorie
    • CJoule
    • DWatt
    Show answer and explanation

    Answer: C) Joule

    Large values are given in kilojoules; 1 kcal = 4.18 kJ. Source: Chemistry 11 KPK (taleem360.com), p. 337.

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