Thermodynamics AQA A Level

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

• 1/2 I₂(s) → I(g)

• I₂(s) → 2I(g)

• 1/2 I₂(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 has the most covalent character?

• MgF₂

• MgBr₂

• AlF₃

• AlBr₃

In which one of the following reactions is there a decrease in entropy?

• [Fe(H₂O)₆]³⁺(aq) + 3C₂O₄^2- (aq) → [Fe(C₂O₄)₃]³⁻(aq) + 6H₂O(l)

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

• [CoCl₄]²⁻(aq) + 6H₂O(l) → [Co(H₂O)₆]²⁺(aq) + 4Cl⁻ (aq)

• Na₂CO₃(s) + 2H⁺(aq) → 2Na⁺(aq) + CO₂(g) + H₂O(l)

This question relates to the equilibrium gas-phase synthesis of sulphur trioxide:

2SO₂(g) + O₂(g) = 2SO₃(g) (the = shows double arrows)

Thermodynamic data for the components of this equilibrium are shown in the image. This equilibrium, at a temperature of 585 K and a total pressure of 540 kPa, occurs in a vessel of volume 1.80 dm³. At equilibrium, the vessel contains 0.0500 mol of SO₂(g), 0.0800 mol of O₂(g) and 0.0700 mol of SO₃(g). The standard entropy change for this reaction is

• −222 J K⁻¹ mol⁻¹

• −195 J K⁻¹ mol⁻¹

• −186 J K⁻¹ mol⁻¹

• +198 J K⁻¹ mol⁻¹

he following information concerns the equilibrium gas-phase synthesis of methanol. CO(g) + 2H₂(g) = CH₃OH(g)

At equilibrium, when the temperature is 68 °C, the total pressure is 1.70 MPa.

The number of moles of CO, H₂ and CH₃OH present are 0.160, 0.320 and 0.180, respectively.

Thermodynamic data are given. The standard entropy change for this reaction is?

• −220 J K⁻¹ mol⁻¹

• +220 J K⁻¹ mol⁻¹

• −89 J K⁻¹ mol⁻¹

• +89 J K⁻¹ mol⁻¹

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

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

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

Refer to the following reaction

H₂(g) + I₂(g) = 2HI(g)

ΔH = −11 kJ mol⁻¹, ΔS = +20 J K⁻¹ mol⁻¹

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.