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Use the data in Table 1 to calculate a value for the electron affinity of chlorine - AQA - A-Level Chemistry - Question 1 - 2020 - Paper 1
Question 1
Use the data in Table 1 to calculate a value for the electron affinity of chlorine. Enthalpy change / kJ mol⁻¹ First ionisation energy of strontium +548 Second ion... show full transcript
Worked Solution & Example Answer:Use the data in Table 1 to calculate a value for the electron affinity of chlorine - AQA - A-Level Chemistry - Question 1 - 2020 - Paper 1
Step 1
Calculate Electron Affinity
Answer
To find the electron affinity of chlorine, we can utilize Hess's law along with the enthalpy changes provided in Table 1. The Born-Haber cycle equation can be expressed as:
Rearranging this gives us:
Substituting the values:
- Enthalpy of formation of strontium chloride ((\Delta H_f^\circ)): -828 kJ mol⁻¹
- Enthalpy of lattice formation of strontium chloride ((\Delta H_{lattice})): -2112 kJ mol⁻¹
- Enthalpy of atomisation of strontium ((\Delta H_{atom, Sr})): +164 kJ mol⁻¹
- First ionisation energy of strontium ((\Delta H_{ion, 1})): +548 kJ mol⁻¹
- Second ionisation energy of strontium ((\Delta H_{ion, 2})): +1060 kJ mol⁻¹
Substituting these values into the rearranged equation yields:
Calculating step-by-step:
- Calculate the sum of ionization energies: (\Delta H_{ion} = 164 + 548 + 1060 = 1772)
- Substitute this into the equation: (\Delta H_{EA} = -828 - 2112 - 1772 = -3712)
Thus,
Electron affinity of chlorine is approximately -3712 kJ mol⁻¹.