Lesson 3.2.1

3.2.1 Enthalpy changes Quiz: OCR Chemistry, Unit 2

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.2.1, Enthalpy changes: 20 multiple choice questions for the OCR Chemistry (H432), Unit 2: Periodic table and energy, written with Revision Ninja.

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The 20 questions

  1. What sign is given to the enthalpy change, ΔH, of an exothermic reaction?

    • Positive
    • Zero
    • Variable
    • Negative

  2. In an enthalpy profile diagram for an endothermic reaction, where are the products positioned relative to reactants?

    • Higher enthalpy
    • Zero enthalpy
    • Equal enthalpy
    • Lower enthalpy

  3. What term describes the minimum energy required for a chemical reaction to take place?

    • Lattice energy
    • Activation energy
    • Enthalpy change
    • Bond enthalpy

  4. Standard enthalpy of formation is defined for the formation of how many moles of a compound?

    • Variable moles
    • Two moles
    • Zero moles
    • One mole

  5. Standard enthalpy of combustion is defined for the complete burning of how many moles of a substance?

    • Variable moles
    • One mole
    • Two moles
    • Half a mole

  6. What standard conditions are commonly taken for enthalpy changes?

    • 100 kPa and 298 K
    • 101 kPa and 273 K
    • 100 kPa and 373 K
    • 1 atm and 0 K

  7. Standard enthalpy of neutralisation is defined for the formation of how many moles of water?

    • Half a mole
    • Variable moles
    • One mole
    • Two moles

  8. 50.0 g of water is heated, and its temperature rises by 5.0 K. Using q = mc∆T with c = 4.18 J g-1 K-1, what is the heat absorbed?

    • 2090 J
    • 1045 J
    • 10450 J
    • 209 J

  9. 0.50 g of ethanol (Mr = 46) burns and heats 100 g of water by 10.0 K (c = 4.18 J g-1 K-1). What is the approximate enthalpy of combustion per mole?

    • -38.5 kJ mol-1
    • -385 kJ mol-1
    • -3850 kJ mol-1
    • +385 kJ mol-1

  10. Using average bond enthalpies C-H 412, Cl-Cl 242, C-Cl 346 and H-Cl 431 kJ mol-1, what is the enthalpy change for CH4 + Cl2 → CH3Cl + HCl?

    • -123 kJ mol-1
    • +654 kJ mol-1
    • +123 kJ mol-1
    • -777 kJ mol-1

  11. Which process characterises the energy change in an exothermic reaction?

    • Bond breaking
    • Electron transfer
    • Bond making
    • Proton transfer

  12. Why does an actual bond enthalpy often differ from an average bond enthalpy value?

    • Chemical environment varies
    • Activation energy changes
    • Standard pressure varies
    • Elements change state

  13. Given ΔfH(CO2) = -394 kJ mol-1 and ΔfH(CO) = -111 kJ mol-1, what is ΔrH for CO + ½O2 → CO2?

    • -505 kJ mol-1
    • -111 kJ mol-1
    • +283 kJ mol-1
    • -283 kJ mol-1

  14. Given ΔcH(C2H4) = -1411, ΔcH(H2) = -286 and ΔcH(C2H6) = -1560 kJ mol-1, what is ΔrH for C2H4 + H2 → C2H6?

    • -1560 kJ mol-1
    • +137 kJ mol-1
    • -137 kJ mol-1
    • -1697 kJ mol-1

  15. What is the main experimental error causing low enthalpy values in simple calorimetry?

    • Incomplete combustion only
    • Heat loss to surroundings
    • Using a glass beaker
    • Incorrect thermometer calibration

  16. How much energy, in kJ per gram, does ethanol (Mr = 46, ΔcH = -1367 kJ mol-1) release on complete combustion?

    • 1367 kJ g-1
    • 2.97 kJ g-1
    • 29.7 kJ g-1
    • 62.9 kJ g-1

  17. What effect does adding a catalyst have on the overall enthalpy change of a reaction?

    • Reverses sign of ΔH
    • Decreases ΔH
    • No effect
    • Increases ΔH

  18. What is the standard enthalpy change of formation of an element in its standard state?

    • Zero
    • Negative
    • Variable
    • Positive

  19. What type of reaction is combustion, characterised by a negative enthalpy change?

    • Reversible
    • Exothermic
    • Endothermic
    • Isothermal

  20. On an enthalpy profile diagram, activation energy is measured from reactants to which point?

    • The baseline
    • The minimum
    • The products
    • The peak

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