3.1.8 Thermodynamics (A-level only)

Which equation represents the process that occurs when the standard enthalpy of atomisation of iodine is measured?

• 0.5I₂(s) → I(g)

• I₂(s) → 2I(g)

• 0.5I₂(g) → I(g)

• I₂(g) → 2I(g)

Lattice enthalpy values can be obtained from Born–Haber cycles and by calculations based on a perfect ionic model.

Which compound shows the greatest percentage difference between these two values?

• CsF

• CsI

• LiF

• LiI

Which one of the following statements is not correct?

• The first ionisation energy of iron is greater than its second ionisation energy.

• The magnitude of the lattice enthalpy of magnesium oxide is greater than that of barium oxide.

• The oxidation state of iron in [Fe(CN)₆]³⁻ is greater than the oxidation state of copper in [CuCl₂]⁻

• The boiling point of C₃H₈ is lower than that of CH₃CH₂OH

Which one of the following has the most covalent character?

• MgF₂

• MgBr₂

• AlF₃

• AlBr₃

A reaction is exothermic and has a negative entropy change.

Which statement is correct?

• The reaction is always feasible

• The reaction is feasible above a certain temperature

• The reaction is feasible below a certain temperature

• The reaction is never feasible

Which one of the equations below represents a reaction that is feasible at all temperatures?

• P(s) → Q(s) + R(g) endothermic

• 2L(g) + M(g) → 2N(g) exothermic

• S(g) → 2T(g) exothermic

• A(g) + B(g) → C(g) endothermic

Which one of the following reactions in aqueous solution has the most positive change in entropy?

• [Cu(H₂O)₆]²⁺ + 4NH₃ → [Cu(NH₃)₄(H₂O)₂]²⁺ + 4H₂O

• [Cu(H₂O)₆]²⁺ + 4Cl⁻ → [CuCl₄]²⁻ + 6H₂O

• [Cu(H₂O)₆]²⁺ + EDTA⁴⁻ → [Cu(EDTA)]²⁻ + 6H₂O

• [Cu(H₂O)₆]²⁺ + 2H₂NCH₂CH₂NH₂ → [Cu(H₂NCH₂CH₂NH₂)₂(H₂O)₂]²⁺ + 4H₂O

Refer to the reaction in the image

Which one of the following statements is correct?

• This is a redox reaction.

• The reaction is not feasible below 298 K

• At equilibrium, the yield of hydrogen iodide is changed by increasing the pressure.

• At equilibrium, the yield of hydrogen iodide increases as the temperature is increased.

This question is about the reaction given below.

CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g)

Enthalpy data for the reacting species are given in the table

Which one of the following statements is not correct?

• The value of K_p changes when the temperature changes.

• The activation energy decreases when the temperature is increased.

• The entropy change is more positive when the water is liquid rather than gaseous.

• The enthalpy change is more positive when the water is liquid rather than gaseous.

Using the information below, answer this question.

Fe₂O₃(s) + 3H₂(g) → 2Fe(s) + 3H₂O(g)

ΔH= +96 kJ mol⁻¹, ΔS = +138 J K⁻¹ mol⁻¹

The standard entropy value for steam is

• +332 J K⁻¹ mol⁻¹

• +189 J K⁻¹ mol⁻¹

• +145 J K⁻¹ mol⁻¹

• +85 J K⁻¹ mol⁻¹