State the meaning of the term enthalpy change. This question is about enthalpy changes for calcium chloride and magnesium chloride. Figure 1 shows an incomplete Born-Haber cycle for the formation of calcium chloride. Complete Figure 1 by writing the formulas, including state symbols, of the appropriate species on each of the three blank lines. Table 1 shows some enthalpy data. Use Figure 1 and the data in Table 1 to calculate a value for the enthalpy of lattice dissociation of calcium chloride. Enthalpy of lattice dissociation _____________ kJ mol⁻¹ Magnesium chloride dissolves in water. Give an equation, including state symbols, to represent the process that occurs when the enthalpy of solution of magnesium chloride is measured. Table 2 shows some enthalpy data. Use your answer to Question 01.4 and the data in Table 2 to calculate a value for the enthalpy of solution of magnesium chloride. Enthalpy of solution ______________ kJ mol⁻¹ The enthalpy of hydration of Ca²⁺(g) is -1650 kJ mol⁻¹. Suggest why this value is less exothermic than that of Mg²⁺(g).

A-Level AQA Chemistry Energetics: State the meaning of the term en

State the meaning of the term enthalpy change - AQA - A-Level Chemistry - Question 1 - 2021 - Paper 1

Question 1

State the meaning of the term enthalpy change. This question is about enthalpy changes for calcium chloride and magnesium chloride. Figure 1 shows an incomplete Bo... show full transcript

Worked Solution & Example Answer:State the meaning of the term enthalpy change - AQA - A-Level Chemistry - Question 1 - 2021 - Paper 1

Step 1

State the meaning of the term enthalpy change.

96%

114 rated

Answer

Enthalpy change refers to the heat energy change that occurs in a system at constant pressure during a chemical or physical process.

Step 2

Complete Figure 1 by writing the formulas, including state symbols, of the appropriate species on each of the three blank lines.

99%

104 rated

Answer

$ext{Ca}^{2+}(g)$
$ext{Cl}_2(g)$
$ext{CaCl}_2(s)$

Step 3

Use Figure 1 and the data in Table 1 to calculate a value for the enthalpy of lattice dissociation of calcium chloride.

96%

101 rated

Answer

From the Born-Haber cycle, the enthalpy of lattice dissociation can be calculated using Hess's law:

$ext{Enthalpy of lattice dissociation} = ext{Enthalpy of formation} + ext{Enthalpy of atomization of Ca} + ext{First ionization energy of Ca} + ext{Second ionization energy of Ca} + ext{Enthalpy of atomization of Cl} + ext{Electron affinity of Cl}$

Calculating:

$= -795 + 193 + 590 + 1150 + 121 - 364 = -5 ext{ kJ mol}^{-1}$

Step 4

Give an equation, including state symbols, to represent the process that occurs when the enthalpy of solution of magnesium chloride is measured.

98%

120 rated

Answer

$ext{MgCl}_2(s) + ext{H}_2O(l) ightarrow ext{Mg}^{2+}(aq) + 2 ext{Cl}^-(aq)$

Step 5

Use your answer to Question 01.4 and the data in Table 2 to calculate a value for the enthalpy of solution of magnesium chloride.

97%

117 rated

Answer

Using the equation:

$ext{Enthalpy of solution} = ext{Enthalpy of hydration of Mg}^{2+} + ext{Enthalpy of hydration of Cl} - ext{Enthalpy of lattice dissociation}$

Substituting the values:

$= -1920 + (2 imes -364) - 2493 = -1920 - 728 - 2493 = -4141 ext{ kJ mol}^{-1}$

Step 6

Suggest why the enthalpy of hydration of Ca²⁺(g) is less exothermic than that of Mg²⁺(g).

97%

121 rated

Answer

The enthalpy of hydration of Ca²⁺(g) is less exothermic due to its larger ionic radius compared to Mg²⁺, resulting in a weaker attraction to water molecules and thus less energy released upon hydration.

State the meaning of the term enthalpy change - AQA - A-Level Chemistry - Question 1 - 2021 - Paper 1

Worked Solution & Example Answer:State the meaning of the term enthalpy change - AQA - A-Level Chemistry - Question 1 - 2021 - Paper 1

State the meaning of the term enthalpy change.

Complete Figure 1 by writing the formulas, including state symbols, of the appropriate species on each of the three blank lines.

Use Figure 1 and the data in Table 1 to calculate a value for the enthalpy of lattice dissociation of calcium chloride.

Give an equation, including state symbols, to represent the process that occurs when the enthalpy of solution of magnesium chloride is measured.

Use your answer to Question 01.4 and the data in Table 2 to calculate a value for the enthalpy of solution of magnesium chloride.

Suggest why the enthalpy of hydration of Ca²⁺(g) is less exothermic than that of Mg²⁺(g).

Join the A-Level students using SimpleStudy...