Concept:The standard enthalpy of formation (\( \Delta H_f^\circ \)) is the enthalpy change associated with the creation of exactly 1 mole of a compound directly from its constituent elements in their standard states at STP.
Formula:$$ Mg_{(s)} + \frac{1}{2}O_{2(g)} \rightarrow MgO_{(s)} $$
Solution:- Magnesium (\( Mg \)) and Oxygen (\( O_2 \)) are in their standard elemental states.
- They combine to form exactly 1 mole of the solid compound Magnesium Oxide (\( MgO \)).
- Because it represents the formation of a compound from its raw elements, the heat change (\( -692 \text{ kJ/mol} \)) is defined as the standard enthalpy of formation, \( \Delta H_f^\circ \).
Why other options are incorrect:It is not \( \Delta H_{at} \) (atomization) because a solid compound is formed. It is not \( \Delta H_n \) (neutralization) because there is no acid/base reaction producing water. It is not \( \Delta H_{sol} \) (solution) because no solute is dissolving in a solvent.
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