10-minute Quiz : Chapter 35 Hess’s Law

For which of the following reactions must its enthalpy change be determined by indirect method?

• A. N₂(g) + 2H₂(g) → N₂H₄(g)
• B. CH₃CH₂CH₂CH₂CH₃(l) + 8O₂(g) → 5CO₂(g) + 6H₂O(l)
• C. MgO(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂O(l)
• D. CH₃COOH(aq) + NH₃(aq) → CH₃COONH₄(aq)

The equation represents the complete combustion of cyclohexane.

• A. +127 kJ mol⁻¹
• B. +3240 kJ mol⁻¹
• C. –156.2 kJ mol⁻¹
• D. –4599 kJ mol⁻¹

Given:

P₄(s) + 3O₂(g) → P₄O₆(s)　　ΔH = a kJ mol⁻¹

P₄(s) + 5O₂(g) → P₄O₁₀(s)　　ΔH = b kJ mol⁻¹

What is the enthalpy change when one mole of P₄O₆ is oxidized by oxygen to form P₄O₁₀?

• A. a + b

• B. 2a − b

• C. a − b

• D. b − a

Given the data as shown. What is the standard enthalpy change of the hydrolysis of sulphur tetrafluoride?

SF₄(g) + 2H₂O(l) → SO₂(g) + 4HF(g)

• A. +478.9 kJ mol⁻¹
• B. −478.9 kJ mol⁻¹
• C. +55.2 kJ mol⁻¹
• D. −55.2 kJ mol⁻¹

Consider the enthalpy change cycle. Which of the relationships is correct?

• A
• B
• C
• D

The following equation represents a reaction occurred in a catalytic converter.

2NO(g) + 2CO(g) → N₂(g) + 2CO₂(g)

Which of the following information are needed to calculate the enthalpy change of the above reaction by applying Hess’s Law?

(1) Enthalpy change of combustion of carbon monoxide

(2) Enthalpy change of formation of nitrogen monoxide

(3) Enthalpy change of formation of carbon dioxide

• A. (1) and (2) only
• B. (1) and (3) only
• C. (2) and (3) only
• D. (1), (2) and (3)

The enthalpy changes of two reactions involving hydrogen are as follows:

C(graphite) + 2H₂(g) → CH₄(g)　　ΔH₁ = −75 kJ mol⁻¹

H₂(g) → 2H(g)　　　　　　　　　ΔH₂ = +436 kJ mol⁻¹

What is the enthalpy change of the following reaction?

CH₄(g) → C(graphite) + 4H(g)

• A. −947 kJ mol⁻¹
• B. +361 kJ mol⁻¹
• C. +511 kJ mol⁻¹
• D. +947 kJ mol⁻¹

The standard enthalpy changes of combustion of ethene, graphite and hydrogen are −1411.2 kJ mol⁻¹, −393.5 kJ mol⁻¹ and −285.8 kJ mol⁻¹ respectively. What is the standard enthalpy change of formation of ethene?

• A. +52.6 kJ mol⁻¹
• B. −52.6 kJ mol⁻¹
• C. +731.9 kJ mol⁻¹
• D. −731.9 kJ mol⁻¹

Consider the enthalpy level diagram as shown.

• A. (1) and (2) only
• B. (1) and (3) only
• C. (2) and (3) only
• D. (1), (2) and (3)

Consider the following statements and choose the best answer:

1st statement

The thermite reaction between aluminium and iron(III) oxide is highly exothermic.

2nd statement

Hess’s Law can be applied when determining the enthalpy change of the thermite reaction between aluminium and iron(III) oxide.

• A. Both statements are true and the 2nd statement is a correct explanation of the 1st statement.
• B. Both statements are true but the 2nd statement is NOT a correct explanation of the 1st statement.
• C. The 1st statement is false but the 2nd statement is true.
• D. Both statements are false.