Lesson 3.1.4.4

3.1.4.4 Bond enthalpies Quiz: AQA Chemistry, Unit 1

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.1.4.4, Bond enthalpies: 20 multiple choice questions for the AQA Chemistry (7405), Unit 1: Physical chemistry, written with Revision Ninja.

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The 20 questions

  1. What is the mean bond enthalpy?

    • The average energy needed to break one mole of a given bond in gaseous molecules, averaged over different compounds
    • The energy released when one mole of gaseous ions forms from atoms, averaged across many different ionic compounds
    • The energy needed to change one mole of a liquid into a gas at its normal boiling point, measured for the liquid alone
    • The energy needed to break one bond in a solid lattice, measured for the bonds in a sample of salt

  2. Breaking bonds is what type of process?

    • Neutral
    • Exothermic
    • Endothermic
    • Isothermal

  3. Forming bonds is what type of process?

    • Endothermic
    • Endothermic only in solids
    • Exothermic
    • Zero energy

  4. Which expression gives delta H using bond enthalpies?

    • Sum of all bond energies in the products
    • Energy of bonds broken minus energy of bonds formed
    • Sum of all bond energies in the reactants only
    • Energy of bonds formed minus energy of bonds broken

  5. Why are mean bond enthalpies used in calculations?

    • Because they measure lattice energy directly, which is the energy of the solid compound
    • Because they are always exact for every molecule, so no averaging is needed in the calculation
    • Because they apply only to ionic bonds, which are the only bonds with a fixed energy value
    • Because the same bond has slightly different energies in different compounds

  6. Which phase do mean bond enthalpy calculations apply to?

    • The aqueous phase only
    • The gaseous phase
    • The liquid phase only
    • The solid phase only

  7. Why are bond enthalpy values only approximate?

    • They change with temperature only in the laboratory, not in the gas phase where they are used
    • They are only measured in aqueous solution, which is where most bonds are broken and formed
    • They are mean values across a range of compounds containing that bond
    • They ignore all of the bonds in a molecule, using just one bond type to represent the whole compound

  8. Using H-H = 436, Cl-Cl = 242 and H-Cl = 431 kJ mol-1, what is delta H for H2 + Cl2 -> 2HCl?

    • +184 kJ mol-1
    • -678 kJ mol-1
    • -1109 kJ mol-1
    • -184 kJ mol-1

  9. Using H-H = 436, F-F = 158 and H-F = 562 kJ mol-1, what is delta H for H2 + F2 -> 2HF?

    • +530 kJ mol-1
    • -1124 kJ mol-1
    • -594 kJ mol-1
    • -530 kJ mol-1

  10. Using C-H = 413, Cl-Cl = 242, C-Cl = 328 and H-Cl = 431 kJ mol-1, what is delta H for CH4 + Cl2 -> CH3Cl + HCl?

    • -759 kJ mol-1
    • +104 kJ mol-1
    • -655 kJ mol-1
    • -104 kJ mol-1

  11. Which bond needs the most energy to break: C-C (348), C=C (612) or C≡C (838) kJ mol-1?

    • C=C
    • C≡C
    • All are equal
    • C-C

  12. When is a reaction endothermic according to bond enthalpy calculations?

    • When the energy released forming bonds exceeds the energy absorbed, so the reaction gives out heat
    • When only bond breaking releases energy, and bond making always takes in energy from the surroundings
    • When the energy absorbed to break bonds is greater than the energy released when new bonds form
    • When the two energies are exactly equal, so no net heat is exchanged with the surroundings

  13. Using C=C = 612, H-H = 436, C-C = 348 and C-H = 413 kJ mol-1, what is delta H for C2H4 + H2 -> C2H6?

    • -1048 kJ mol-1
    • -1174 kJ mol-1
    • +126 kJ mol-1
    • -126 kJ mol-1

  14. What is the enthalpy change for the formation of H2 gas from H atoms, given H-H = 436 kJ mol-1?

    • +436 kJ mol-1
    • -218 kJ mol-1
    • +218 kJ mol-1
    • -436 kJ mol-1

  15. Which statement about bond breaking and making is correct?

    • Breaking bonds releases energy and making bonds absorbs energy
    • Both breaking and making bonds absorb energy
    • Neither breaking nor making bonds involves energy
    • Breaking bonds absorbs energy and making bonds releases energy

  16. Why does methane have a different C-H bond enthalpy from ethane?

    • Ethane has no C-H bonds, because its carbon atoms are joined only by single covalent bonds
    • Mean bond enthalpies vary across compounds, so a bond's enthalpy depends on the molecule it sits in
    • Methane is an ionic compound, so its C-H bonds are weaker than the bonds in covalent ethane
    • C-H bonds are identical in all compounds, so methane and ethane have exactly the same bond enthalpy

  17. Using N≡N = 945, H-H = 436 and N-H = 391 kJ mol-1, what is delta H for N2 + 3H2 -> 2NH3?

    • +93 kJ mol-1
    • -93 kJ mol-1
    • -2253 kJ mol-1
    • -2346 kJ mol-1

  18. Why are mean bond enthalpy calculations restricted to gaseous species?

    • Gases have no bonds, so the calculation can only be applied to liquids and solids in practice
    • Bond enthalpies can only be measured in liquids, where the molecules are close enough to react
    • Solid lattices always need water to form bonds, so only aqueous reactions can be calculated
    • Bond enthalpies refer to bonds in isolated gaseous molecules, so intermolecular energies would distort the values

  19. Using C=C = 612, H-Cl = 431, C-C = 348, C-H = 413 and C-Cl = 328 kJ mol-1, what is the estimated delta H for C2H4 + HCl -> C2H5Cl?

    • +46 kJ mol-1
    • -1089 kJ mol-1
    • -1043 kJ mol-1
    • -46 kJ mol-1

  20. A reaction needs 1200 kJ to break bonds and releases 1350 kJ when bonds form. What is delta H?

    • -2550 kJ mol-1
    • +150 kJ mol-1
    • -150 kJ mol-1
    • +2550 kJ mol-1

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