Energetics AQA A Level Chemistry

Calculate the enthalpy change, in kJ, for this dissociation of mole of propan-1-ol.

C₃H₇OH(g) ⟶ 3C(g) + 8H(g) + O(g)

• −4751

• −4403

• +4403

• +4751

Consider the reactions

C₂H₄(g) + 2O₂(g) → 2CO(g) + 2H₂O(g)                            ∆H = −758 kJ mol⁻¹

2C(s) + 2H₂(g) → C₂H₄(g)                                        ∆H = +52 kJ mol⁻¹

H₂(g) +  O₂(g) → H₂O(g)                                         ∆H = −242 kJ mol⁻¹

The enthalpy of formation of carbon monoxide is

• −111 kJ mol⁻¹

• −163 kJ mol⁻¹

• −222 kJ mol⁻¹

• -464 kJ mol⁻¹

Nitric acid is produced industrially from ammonia, air and water using the following sequence of reactions:

 

(1)        4NH₃ (g) + 5O₂(g) → 4NO(g) + 6H₂O(g)

∆H = –909 kJ mol⁻¹ 

(2)        2NO(g) + O₂(g) → 2NO₂(g)

∆H  = –115 kJ mol⁻¹

(3)        3NO₂(g) + H₂O(l) → 2HNO₃(aq) + NO(g)

∆H = –117 kJ mol⁻¹ 

Which is the enthalpy change (in kJ mol⁻¹) for the following reaction?

4NH₃(g) + 7O₂(g) → 4NO₂(g) + 6H₂O(g)

• −679

• −794

• −1024

• −1139

Given the following data

C(s) + 2H₂(g) → CH₄(g)                       ∆H = −75 kJ mol⁻¹

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

which one of the following is the enthalpy change, in kJ mol⁻¹, of the reaction below?

CH₄(g) → C(s) + 4H(g)

• −947

• +511

• +797

• +947

In which one of the following reactions is the standard enthalpy change equal to the standard enthalpy of formation of lithium fluoride?

• Li(g) + F(g) → LiF(s)

• Li⁺(g) + F⁻(g) → LiF(s)

• Li⁺(aq) + F⁻(g) → LiF(s)

• Li(s) + 1/2F₂(g) → LiF(s)

Answer explanation

The standard enthalpy of formation of a compound is defined as the enthalpy change when one mole of the compound is formed from its elements in their standard states. In this case, the formation of lithium fluoride (LiF) from lithium in its standard state (solid) and fluorine in its standard state (gas) is the correct choice.

When ethanamide (CH₃CONH₂) burns in oxygen the carbon is converted into carbon dioxide, the hydrogen is converted into water and the nitrogen forms nitrogen gas. Using the data given, which one of the following is a correct value for the enthalpy of combustion of ethanamide?

• −1823 kJ mol⁻¹

• −1183 kJ mol⁻¹

• −1000 kJ mol⁻¹

• −360 kJ mo1⁻¹

Use the information below to answer this question.

        C(s) + O₂(g) → CO₂(g)                 ΔH = −394 kJ mol⁻¹

H₂(g) +  O₂(g) → H₂O(l)                     ΔH = −286 kJ mol⁻¹

    4C(s) + 5H₂(g) → C₄H₁₀(g)               ΔH = −126 kJ mol⁻¹

The standard enthalpy of combustion of butane, in kJ mol⁻¹, is

• −2880

• −2590

• −806

• −554

The data given refer to the industrial production of nitric acid from ammonia. The direct oxidation of ammonia to nitrogen dioxide can be represented by the equation

4NH₃(g) + 7O₂(g) → 4NO₂(g) + 6H₂O(g)

for which the standard enthalpy change, in kJ mol⁻¹, is

• −1139

• −1024

• −794

• −679

Using the data given, which is the correct value for the standard enthalpy of formation for TiCl₄(l)?

• −1538 kJ mol⁻¹

• −1094 kJ mol⁻¹

• −750 kJ mol⁻¹

• +286 kJ mol⁻¹

Using the information below, answer this question. The standard enthalpy of formation of steam is

• +286 kJ mol⁻¹

• +242 kJ mol⁻¹

• −242 KJ mol⁻¹

• −286 kJ mol⁻¹