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.
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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.
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Answer
extCa2+(g)
extCl2(g)
extCaCl2(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.
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Answer
From the Born-Haber cycle, the enthalpy of lattice dissociation can be calculated using Hess's law:
Suggest why the enthalpy of hydration of Ca²⁺(g) is less exothermic than that of Mg²⁺(g).
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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.
