Energy is required to remove two electrons from Ca to form Cat, and energy is re
ID: 696428 • Letter: E
Question
Energy is required to remove two electrons from Ca to form Cat, and energy is required to add two electrons to O to form O. Yet Cao is stable relative to the free elements. Which statement is the best explanation? (a) The latticeen ergy of CaO is large enough to overcome these processes (b) Cao is a covalent compound, and these processes are ir relevant. (c) CaO has a higher molar mass than either Ca or O. (d) The enthalpy of formation of CaO is small. (e) Cao is sta- ble to atmospheric conditions.Explanation / Answer
Calcium oxide is an ionic compound.
The enthalpy of formation of Calcium oxide is -635.5 KJ/mol, which is very large. Calcium oxide reacts with carbon dioxide in the atmosphere to form calcium carbonate instantly. A compound having higher molar mass has no relationship with it's stability.
The only correct option is the lattice energy of CaO being greater than the sum of electron affinity enthalpy of oxygen and ionisation enthalpy of Calcium.
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