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KMU MDCAT 2024 Chemistry #Ionization Energy #Periodic Trends

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The heat of sublimation of potassium is 98 kJ/mol, the heat of dissociation of bromine gas is 192.5 kJ/mol. The ionization energy of K is 414 kJ/mol. The electron affinity of Br is −334.7 kJ/mol and the heat of formation of KBr is −405.8 kJ/mol. Calculate the lattice energy of KBr. (KMU MDCAT 2024)

Verified Answer & Explanation⌄

Correct Answer: A) −679.3

Concept Explanation

Using the Born–Haber cycle: U = −405.8 − [98 + 96.25 + 414 − 334.7] = about −679.3 kJ mol⁻¹. The negative sign shows energy is released when the ionic lattice forms.

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