Lesson 8.2.1

8.2.1 Enthalpy cycles and Hess's Law Quiz: Pearson Edexcel Chemistry, Unit 8

20 questions

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Lesson 8.2.1, Enthalpy cycles and Hess's Law: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 8: Energetics I, written with Revision Ninja.

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The 20 questions

  1. According to Hess's law, enthalpy change is independent of which factor?

    • Temperature change
    • Final state
    • Reaction route
    • Initial state

  2. Given C(s) + O2(g) -> CO2(g), delta H = -393.5 kJ mol-1, and CO(g) + 1/2 O2(g) -> CO2(g), delta H = -283.0 kJ mol-1, what is delta H for C(s) + 1/2 O2(g) -> CO(g)?

    • -110.5 kJ mol-1
    • -283.0 kJ mol-1
    • +110.5 kJ mol-1
    • -676.5 kJ mol-1

  3. What must direct and indirect routes share in a Hess cycle?

    • Same activation energy
    • Same reaction rate
    • Same start and end
    • Same intermediate steps

  4. What happens to the sign of ΔH when a reaction equation is reversed?

    • It becomes zero
    • It doubles
    • It changes sign
    • It stays positive

  5. What happens to ΔH when all stoichiometry numbers in an equation are doubled?

    • It squares
    • It halves
    • It doubles
    • It stays unchanged

  6. Using enthalpy of formation data, delta Hf of CO2 = -393.5, H2O(l) = -285.8, and C2H5OH(l) = -277.7 kJ mol-1, what is delta Hc of ethanol? C2H5OH + 3O2 -> 2CO2 + 3H2O

    • -1366.7 kJ mol-1
    • +1366.7 kJ mol-1
    • -956.9 kJ mol-1
    • -1088.0 kJ mol-1

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

    • -1 kJ mol⁻¹
    • +1 kJ mol⁻¹1
    • Variable
    • Zero

  8. How do direct and indirect routes compare in total enthalpy change in a Hess cycle?

    • They are equal
    • Direct is greater
    • They are opposite
    • Indirect is greater

  9. Given delta H1 = -285.8 kJ mol-1 for H2 + 1/2 O2 -> H2O(l) and delta H2 = -241.8 kJ mol-1 for H2 + 1/2 O2 -> H2O(g), what is delta H for H2O(l) -> H2O(g)?

    • +241.8 kJ mol-1
    • -527.6 kJ mol-1
    • +44.0 kJ mol-1
    • -44.0 kJ mol-1

  10. What is the enthalpy change for the reaction C(s) + 2H2(g) -> CH4(g), given C(s) + O2 -> CO2 = -393.5, H2 + 1/2 O2 -> H2O(l) = -285.8 and CH4 + 2O2 -> CO2 + 2H2O(l) = -890.3 kJ mol-1? Use Hess's Law.

    • -74.8 kJ mol-1
    • -1569.6 kJ mol-1
    • -890.3 kJ mol-1
    • +74.8 kJ mol-1

  11. Why do chemists construct Hess cycles for certain chemical reactions?

    • Speed up reactions
    • Determine reaction rate
    • Increase reaction yield
    • Calculate unmeasurable enthalpies

  12. What must be identical for all routes in a Hess cycle?

    • Total entropy change
    • Reaction pathway
    • Initial and final states
    • Activation energy barrier

  13. In a Hess cycle using combustion data, where do the enthalpy arrows point?

    • To original reactants
    • To gaseous elements
    • To solid catalysts
    • To combustion products

  14. Given that the enthalpy of combustion of hydrogen is -285.8 kJ mol-1, how much heat is released when 4.00 g of hydrogen (Mr = 2.0) burns to form liquid water?

    • 285.8 kJ
    • 571.6 kJ
    • 142.9 kJ
    • 1143.2 kJ

  15. A student calculates a positive ΔH for an exothermic reaction. What error occurred?

    • Multiplied by volume
    • Incorrect mass unit
    • Incorrect sign reversal
    • Forgot gas constant

  16. What is the standard enthalpy change of formation of oxygen gas, O2(g)?

    • 0 kJ mol⁻¹
    • +100 kJ mol⁻¹
    • +249 kJ mol⁻¹
    • -394 kJ mol⁻¹

  17. What is the enthalpy change for C(s) + 1/2 O2(g) -> CO(g), given C(s) + O2 -> CO2 = -393.5 and CO + 1/2 O2 -> CO2 = -283.0 kJ mol-1, if the second equation is multiplied by -1?

    • -283.0 kJ mol-1
    • -110.5 kJ mol-1
    • -676.5 kJ mol-1
    • +110.5 kJ mol-1

  18. What sign does the enthalpy change ΔH have for an exothermic reaction?

    • Negative
    • Zero
    • Positive
    • Neutral

  19. What is indicated when two Hess cycle routes give conflicting values?

    • Endothermic change
    • Measurement error
    • Activation energy barrier
    • Non-standard conditions

  20. The standard enthalpy of combustion of carbon is -393.5 kJ mol-1. How much heat is released when 6.00 g of carbon (Ar = 12.0) burns completely?

    • 393.5 kJ
    • 196.8 kJ
    • 98.4 kJ
    • 787.0 kJ

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